In a cliff of stiff brown boulder clay, about 20 feet high, on the

banks of the Carmichael Water, Lanarkshire, Professor Geikie observed

a stratified bed of clay about 3 or 4 inches in thickness. About a mile

higher up the stream, he found a series of beds of gravel, sand, and

clay in the true _till_. “A thin seam of _peaty matter_,” he says, “was

observed to run for a few inches along the bottom of a bed of clay and

then disappear, while in a band of fine laminated clay with thin sandy

partings occasional _fragments of mouldering wood_ were found.”[112]

At Chapelhall, near Airdrie, a sand-bed has been extensively mined

under about 114 feet of till. This bed of finely stratified sand

is about 20 feet thick. In it were found lenticular beds of fine

pale-coloured clay containing layers of peat and decaying twigs and

branches. Professor Geikie found the vegetable fibres, though much

decayed, still distinct, and the substance when put into the fire

burned with a dull lambent flame. Underlying these stratified beds, and

forming the floor of the mine, is a deposit of _the true till_ about

24 feet in thickness. In another pit adjoining, the till forming the

floor is 30 feet thick, but it is sometimes absent altogether, so as to

leave the sand beds resting directly on the sandstone and shale of the

coal-measures. At some distance from this sand-pit an old buried river

channel was met with in one of the pit workings. This channel was found

to contain a coating of boulder clay, on which the laminated sands and

clays reposed, showing, as Professor Geikie has pointed out, that this

old channel had been filled with boulder clay, and then re-excavated

to allow of the deposition of the stratified deposits. Over all lay a

thick mantle of boulder clay which buried the whole.

A case somewhat similar was found by Professor Nicol in a cutting on

the Edinburgh and Leith Railway. In many places the till had been

worn into hollows as if part of it had been removed by the action of

running water.[113] One of these hollows, about 5 or 6 feet wide by 3

or 4 feet deep, closely resembled the channel of a small stream. It

was also filled with gravel and sand, in all respects like that found

in such a stream at the present day. It was seen to exhibit the same

characters on both sides of the cutting, but Professor Nicol was unable

to determine how far it may have extended beyond; but he had no doubt

whatever that it had been formed by a stream of water. Over this old

watercourse was a thick deposit of true till.

In reference to the foregoing cases, Professor Geikie makes the

following pertinent remarks:—“Here it is evident that the scooping out

of this channel belongs to the era of the boulder clay. It must have

been effected during a pause in the deposition of the clay, when a run

of water could find its way along the inequalities of the surface of

the clay. This pause must have been of sufficient duration to enable

the runnel to excavate a capacious channel for itself, and leave in it

a quantity of sand and shingle. We can scarcely doubt that when this

process was going on the ground must have been a land surface, and

could not have been under the sea. And lastly, we see from the upper

boulder clay that the old conditions returned, the watercourse was

choked up, and another mass of chaotic boulder clay was tumbled down

upon the face of the country. This indicates that the boulder clay is

not the result of one great catastrophe, but of slow and silent, yet

mighty, forces acting sometimes with long pauses throughout a vast

cycle of time.”[114]

At Craiglockhart Hill, about a mile south of Edinburgh, an extensive

bed of fine sand of from one to three feet in thickness was found

between two distinct masses of true boulder clay or till. The sand was

extensively used for building purposes during the erection of the city

poorhouse a few years ago. In this sand-bed I found a great many tree

roots in the position in which they had grown. During the time of the

excavations I visited the place almost daily, and had every opportunity

of satisfying myself that this sand-bed, prior to the time of the

formation of the upper boulder clay, must have been a land surface

on which the roots had grown. In no case did I find them penetrating

into the upper boulder clay, and in several places I found stones of

the upper clay resting directly on the broken ends of the roots. These

roots were examined by Professor Balfour, but they were so decayed that

he was unable to determine their character.

In digging a foundation for a building in Leith Walk, Edinburgh, a few

years ago, two distinct beds of sand were passed through, the upper,

about 10 feet in thickness, rested upon what appeared to be a denuded

surface of the lower bed. In this lower bed, which evidently had been

a land surface, numbers of tree roots were found. I had the pleasure

of examining them along with my friend Mr. C. W. Peach, who first

directed my attention to them. In no instance were the roots found

in the upper bed. That these roots did not belong to trees which had

grown on the present surface and penetrated to that depth, was further

evident from the fact that in one or two cases we found the roots

broken off at the place where they had been joined to the trunk, and

there the upper sand-bed over them was more than 10 feet in thickness.

If we assume that the roots belonged to trees which had grown on the

present surface, then we must also assume, what no one would be willing

to admit, that the trunks of the trees had grown downwards into the

earth to a depth of upwards of ten feet. I have shown these roots to

several botanists, but none of them could determine to what trees they

belonged. The surface of the ground at the spot in question is 45 feet

above sea-level. Mr. Peach and I have found similar roots in the under

sand-bed at several other places in the same neighbourhood. That they

belong to an inter-glacial period appears probable for the following

reasons:—(1.) This upper sand-bed is overlaid by a tough clay, which

in all respects appears to be the same as the Portobello clay, which

we know belongs to the glacial series. In company with Mr. Bennie,

I found the clay in some places to be contorted in a similar manner

to the Portobello clays. (2.) In a sand-pit about one or two hundred

yards to the west of where the roots were found, the sand-bed was

found contorted in the most extraordinary manner to a depth of about 15

feet. In fact, for a space of more than 30 feet, the bedding had been

completely turned up on end without the fine layers being in the least

degree broken or disarranged, showing that they had been upturned by

some enormous powers acting on a large mass of the sand.

One of the best examples of true till to be met with in the

neighbourhood of Edinburgh is at Redhall Quarry, about three miles to

the south-west of the city. In recently opening up a new quarry near

the old one a bed of peat was found intercalated in the thick mass of

till overlying the rock. The clay overlying and underlying the peat-bed

was carefully examined by Mr. John Henderson,[115] and found to be true

till.

In a quarry at Overtown, near Beith, Ayrshire, a sedimentary bed of

clay, intercalated between two boulder clays, was some years ago

observed by Mr. Robert Craig, of the Glasgow Geological Society. This

bed filled an elliptical basin about 130 yards long, and about 30 yards

broad. Its thickness averaged from one to two feet. This sedimentary

bed rested on the till on the north-east end of the basin, and was

itself overlaid on the south-west end by the upper bed of till. The

clay bed was found to be full of roots and stems of the common hazel.

That these roots had grown in the position in which they were found

was evident from the fact that they were in many places found to pass

into the “cutters” or fissures of the limestone, and were here found

in a flattened form, having in growing accommodated themselves to the

size and shape of the fissures. Nuts of the hazel were plentifully

found.[116]

At Hillhead, some distance from Overtown, there is a similar

intercalated bed full of hazel remains, and a species of freshwater

_Ostracoda_ was detected by Mr. David Robertson.

In a railway cutting a short distance from Beith, Mr. Craig pointed out

to my colleague, Mr. Jack, and myself, a thin layer of peaty matter,

extending for a considerable distance between an upper and lower mass

of till; and at one place we found a piece of oak about four feet in

length and about seven or eight inches in thickness. This oak boulder

was well polished and striated.

Not far from this place is the famous Crofthead inter-glacial bed, so

well known from the description given by Mr. James Geikie and others

that I need not here describe it. I had the pleasure of visiting the

section twice while it was well exposed, once, in company with Mr.

James Geikie, and I do not entertain the shadow of a doubt as to its

true inter-glacial character.

In the silt, evidently the mud of an inter-glacial lake, were found the

upper portion of the skull of the great extinct ox (_Bos primigenius_),

horns of the Irish elk or deer, and bones of the horse. In the detailed

list of the lesser organic remains found in the intercalated peat-bed

by Mr. J. A. Mahony,[117] are the following, viz., three species of

_Desmidaceæ_, thirty-one species of _Diatomaceæ_, eleven species of

mosses, nine species of phanerogamous plants, and several species of

annelids, crustacea, and insects. This list clearly shows that the

inter-glacial period, represented by these remains, was not only mild

and warm, but of considerable duration. Mr. David Robertson found in

the clay under the peat several species of _Ostracoda_.

The well-known Kilmaurs bed of peaty matter in which the remains of

the mammoth and reindeer were found, has now by the researches of the

Geological Survey been proved to be of inter-glacial age.[118]

In Ireland, as shown by Professors Hull and Harkness, the inter-glacial

beds, called by them the “manure gravels,” contain numerous fragments

of shells indicating a more genial climate than prevailed when the

boulder clays lying above and below them were formed.[119]

In Sweden inter-glacial beds of freshwater origin, containing plants,

have been met with by Herr Nathorst and also by Herr Holmström.[120]

In North America Mr. Whittlesey describes inter-glacial beds of blue

clay enclosing pieces of wood, intercalated with beds of hard pan

(till). Professor Newberry found at Germantown, Ohio, an immense bed of

peat, from 12 to 20 feet in thickness, underlying, in some places 30

feet, and in other places as much as 80 feet, of till, and overlying

drift beds. The uppermost layers of the peat contain undecomposed

sphagnous mosses, grasses, and sedges, but in the other portions of

the bed abundant fragments of coniferous wood, identified as red cedar

(_Juniperus virginiana_), have been found. Ash, hickory, sycamore,

together with grape-vines and beech-leaves, were also met with, and

with these the remains of the mastodon and great extinct beaver.[121]

_Inter-glacial Beds of England._—Scotland has been so much denuded by

the ice sheet with which it was covered during the period of maximum

glaciation that little can be learned in this part of the island

regarding the early history of the glacial epoch. But in England,

and more especially in the south-eastern portion of it, matters are

somewhat different. We have, in the Norwich Crag and Chillesford beds,

a formation pretty well developed, which is now generally regarded as

lying at the base of the Glacial Series. That this formation is of a

glacial character is evident from the fact of its containing shells of

a northern type, such as _Leda lanceolata_, _Cardium Groènlandicum_,

_Lucina borealis_, _Cyprina Islandica_, _Panopæa Norvegica_, and

_Mya truncata_. But the glacial character of the formation is

more strikingly brought out, as Sir Charles Lyell remarks, by the

predominance of such species as _Rhynchonella psittacea_, _Tellina

calcarea_, _Astarte borealis_, _Scalaria Groènlandica_, and _Fusus

carinatus_.

_The “Forest Beds.”_—Immediately following this in the order of

time comes the famous “Forest Bed” of Cromer. This buried forest has

been traced for more than forty miles along the coast from Cromer to

near Kessengland, and consists of stumps of trees standing erect,

attached to their roots, penetrating the original soil in which they

grew. Here and in the overlying fluvio-marine beds we have the first

evidence of at least a temperate, if not a warm, inter-glacial period.

This is evident from the character of the flora and fauna belonging

to these beds. Among the trees we have, for example, the Scotch and

spruce fir, the yew, the oak, birch, the alder, and the common sloe.

There have also been found the white and yellow water-lilies, the

pond-weed, and others. Amongst the mammalia have been met with the

_Elephas meridionalis_, also found in the Lower Pliocene beds of the

Val d’Arno, near Florence; _Elephas antiquus_, _Hippopotamus major_,

_Rhinoceros Etruscus_, the two latter Val d’Arno species, the roebuck,

the horse, the stag, the Irish elk, the _Cervus Polignacus_, found

also at Mont Perrier, France, _C. verticornis_, and _C. carnutorum_,

the latter also found in Pliocene strata of St. Prest, France. In

the fluvio-marine series have been found the _Cyclas omnica_ and the

_Paludina marginata_, a species of mollusc still found in the South of

France, but no longer inhabiting the British Isles.

Above the forest bed and fluvio-marine series comes the well-known

unstratified Norwich boulder till, containing immense blocks 6 or 8

feet in diameter, many of which must have come from Scandinavia, and

above the unstratified till are a series of contorted beds of sand and

gravel. This series may be considered to represent a period of intense

glaciation. Above this again comes the middle drift of Mr. Searles

Wood, junior, yielding shells which indicate, as is now generally

admitted, a comparatively mild condition of climate. Upon this middle

drift lies the upper boulder clay, which is well developed in South

Norfolk and Suffolk, and which is of unmistakable glacial origin. Newer

than all these are the Mundesley freshwater beds, which lie in a hollow

denuded out of the foregoing series. In this formation a black peaty

deposit containing seeds of plants, insects, shells, and scales and

bones of fishes, has been found, all indicating a mild and temperate

condition of climate. Among the shells there is, as in the forest bed,

the _Paludina marginata_. And that an arctic condition of things in

England followed is believed by Mr. Fisher and others, on the evidence

of the “Trail” described by the former observer.

_Cave and River Deposits._—Evidence of the existence of warm periods

during the glacial epoch is derived from a class of facts which

have long been regarded by geologists as very puzzling, namely, the

occurrence of mollusca and mammalia of a southern type associated

in England and on the continent with those of an extremely arctic

character. For example, _Cyrena fluminalis_ is a shell which does not

live at present in any European river, but inhabits the Nile and parts

of Asia, especially Cashmere. _Unio littoralis_, extinct in Britain,

is still abundant in the Loire; _Paludina marginata_ does not exist

in this country. These shells of a southern type have been found in

post-tertiary deposits at Gray’s Thurrock, in Essex; in the valley

of the Ouse, near Bedford; and at Hoxne, in Suffolk, associated with

a _Hippopotamus_ closely allied to that now inhabiting the Nile, and

_Elephas antiquus_, an animal remarkable for its southern range.

Amongst other forms of a southern type which have been met with in

the cave and river deposits, are the spotted hyæna from Africa,

an animal, says Mr. Dawkins, identical, except in size, with the

cave hyæna, the African elephant (_E. Africanus_), and the _Elephas

meridionalis_, the great beaver (_Trogontherium_), the cave hyæna

(_Hyæna spelæa_), the cave lion (_Felis leo_, var. _spelæa_), the lynx

(_Felis lynx_), the sabre-toothed tiger (_Machairodus latidens_), the

rhinoceros (_Rhinoceros megarhinus_ and _R. leptorhinus_). But the

most extraordinary thing is that along with these, associated in the

same beds, have been found the remains of such animals of an arctic

type as the glutton (_Gulo luscus_), the ermine (_Mustela erminea_),

the reindeer (_Cervus tarandus_), the musk-ox or musk-sheep (_Ovibos

moschatus_), the aurochs (_Bison priscus_), the woolly rhinoceros

(_Rhinoceros tichorhinus_), the mammoth (_Elephas primigenius_), and

others of a like character. According to Mr. Boyd Dawkins, these

southern animals extended as far north as Yorkshire in England, and

the northern animals as far south as the latitude of the Alps and

Pyrenees.[122]

_The Explanation of the Difficulty._—As an explanation of these

puzzling phenomena, I suggested, in the Philosophical Magazine for

November, 1868, that these southern animals lived in our island during

the warm periods of the glacial epoch, while the northern animals

lived during the cold periods. This view I am happy to find has lately

been supported by Sir John Lubbock; further, Mr. James Geikie, in his

“Great Ice Age,” and also in the Geological Magazine, has entered so

fully into the subject and brought forward such a body of evidence

in support of it, that, in all probability, it will, ere long, be

generally accepted. The only objection which has been advanced, so far

as I am aware, deserving of serious consideration, is that by Mr. Boyd

Dawkins, who holds that if these migrations had been _secular_ instead

of seasonal, as is supposed by Sir Charles Lyell and himself, the

arctic and southern animals would now be found in separate deposits.

It is perfectly true that if there had been only one cold and one warm

period, each of geologically immense duration, the remains might, of

course, be expected to have been found in separate beds; but when

we consider that the glacial epoch consisted of a long _succession

of alternate cold and warm periods_, of not more than ten or twelve

thousand years each, we can hardly expect that in the river deposits

belonging to this long cycle we should be able to distinguish the

deposits of the cold periods from those of the warm.

_Shell Beds._—Evidence of warm inter-glacial periods may be justly

inferred from the presence of shells of a southern type which have been

found in glacial beds, of which some illustrations follow.

In the southern parts of Norway, from the present sea-level up to 500

feet, are found glacial shell beds, similar to those of Scotland. In

these beds _Trochus magus_, _Tapes decussata_, and _Pholas candida_

have been found, shells which are distributed between the Mediterranean

and the shores of England, but no longer live round the coasts of

Norway.

At Capellbacken, near Udevalla, in Sweden, there is an extensive bed of

shells 20 to 30 feet in thickness. This formation has been described

by Mr. Gwyn Jeffreys.[123] It consists of several distinct layers,

apparently representing many epochs and conditions. Its shells are of a

highly arctic character, and several of the species have not been found

living south of the arctic circle. But the remarkable circumstance

is that it contains _Cypræa lurida_, a Mediterranean shell, which

Mr. Jeffreys, after some hesitation, believed to belong to the bed.

Again, at Lilleherstehagen, a short distance from Capellbacken,

another extensive deposit is exposed. “Here the upper layer,” says Mr.

Jeffreys, “gives a singular result. Mixed with the universal _Trophon

clathratus_ (which is a high northern species, and found living only

within the arctic circle) are many shells of a southern type, such are

_Ostrea edulis_, _Tapes pullastra_, _Corbula gibba_, and _Aporrhais

pes-pelicani_.”

At Kempsey, near Worcester, a shell bed is described by Sir R.

Murchison in his “Silurian System” (p. 533), in which _Bulla ampulla_

and a species of _Oliva_, shells of a southern type, have been found.

A case somewhat similar to the above is recorded by the Rev. Mr.

Crosskey as having been met with in Scotland at the Kyles of Bute.

“Among the Clyde beds, I have found,” he says, “a layer containing

shells, in which those of a more southern type appear to exist in

greater profusion and perfection than even in our present seas. It is

an open question,” he continues, “whether our climate was not slightly

warmer than it is now between the glacial epoch and the present

day.”[124]

In a glacial bed near Greenock, Mr. A. Bell found the fry of living

Mediterranean forms, viz., _Conus Mediterraneus_ and _Cardita trapezia_.

Although deposits containing shells of a temperate or of a southern

type in glacial beds have not been often recorded, it by no means

follows that such deposits are actually of rare occurrence. That

glacial beds should contain deposits indicating a temperate or a

warm condition of climate is a thing so contrary to all preconceived

opinions regarding the sequence of events during the glacial epoch,

that most geologists, were they to meet with a shell of a southern

type in one of those beds, would instantly come to the conclusion that

its occurrence there was purely accidental, and would pay no special

attention to the matter.

_Evidence derived from “Borings.”_—With the view of ascertaining if

additional light would be cast on the sequence of events, during the

formation of the boulder clay, by an examination of the journals of

bores made through a great depth of surface deposits, I collected,

during the summer of 1867, about two hundred and fifty such records,

put down in all parts of the mining districts of Scotland. An

examination of these bores shows most conclusively that the opinion

that the boulder clay, or lower till, is one great undivided formation,

is wholly erroneous.

These two hundred and fifty bores represent a total thickness of 21,348

feet, giving 86 feet as the mean thickness of the deposits passed

through. Twenty of these have one boulder clay, with beds of stratified

sand or gravel beneath the clay; twenty-five have _two_ boulder clays,

with stratified beds of sand and gravel between; ten have _three_

boulder clays; one has _four_ boulder clays; two have _five_ boulder

clays; and no one has fewer than _six_ separate masses of boulder

clay, with stratified beds of sand and gravel between; sixteen have

two or three separate boulder clays, differing altogether in colour

and hardness, without any stratified beds between. We have, therefore,

out of two hundred and fifty bores, seventy-five of them representing

a condition of things wholly different from that exhibited to the

geologist in ordinary sections.

The full details of the character of the deposits passed through by

these bores, and their bearing on the history of the glacial epoch,

have been given by Mr. James Bennie, in an interesting paper read

before the Glasgow Geological Society,[125] to which I would refer all

those interested in the subject of surface geology.

The evidence afforded by these bores of the existence of warm

inter-glacial periods will, however, fall to be considered in a

subsequent chapter.[126]

Another important and unexpected result obtained from these bores to

which we shall have occasion to refer, was the evidence which they

afforded of a Continental Period.

_Striated Pavements._—It has been sometimes observed that in horizontal

sections of the boulder clay, the stones and boulders are all striated

in one uniform direction, and this has been effected over the original

markings on the boulders. It has been inferred from this that a pause

of long duration must have taken place in the formation of the boulder

clay, during which the ice disappeared and the clay became hardened

into a solid mass. After which the old condition of things returned,

glaciers again appeared, passed over the surface of the hardened clay

with its imbedded boulders, and ground it down in the same way as they

had formerly done the solid rocks underneath the clay.

An instance of striated pavements in the boulder clay was observed by

Mr. Robert Chambers in a cliff between Portobello and Fisherrow. At

several places a narrow train of blocks was observed crossing the line

of the beach, somewhat like a quay or mole, but not more than a foot

above the general level. All the blocks _had flat sides uppermost,

and all the flat sides were striated in the same direction_ as that

of the rocky surface throughout the country. A similar instance was

also observed between Leith and Portobello. “There is, in short,” says

Mr. Chambers, “a surface of the boulder clay, deep down in the entire

bed, which, to appearance, has been in precisely the same circumstances

as the fast rock surface below had previously been. It has had in its

turn to sustain the weight and abrading force of the glacial agent,

in whatever form it was applied; and the additional deposits of the

boulder clay left over this surface may be presumed to have been formed

by the agent on that occasion.”[127]

Several cases of a similar character were observed by Mr. James

Smith, of Jordanhill, on the beach at Row, and on the shore of the

Gareloch.[128] Between Dunbar and Cockburnspath, Professor Geikie found

along the beach, for a space of 30 or 40 square yards, numbers of large

blocks of limestone with flattened upper sides, imbedded in a stiff red

clay, and all striated in one direction. On the shores of the Solway he

found another example.[129]

The cases of striated pavements recorded are, however, not very

numerous. But this by no means shows that they are of rare occurrence

in the boulder clay. These pavements, of course, are to be found only

in the interior of the mass, and even there they can only be seen

along a horizontal section. But sections of this kind are rarely to be

met with, for river channels, quarries, railway cuttings, and other

excavations of a similar character which usually lay open the boulder

clay, exhibit vertical sections only. It is therefore only along the

sea-shore, as Professor Geikie remarks, where the surface of the clay

has been worn away by the action of the waves, that opportunities have

hitherto been presented to the geologist for observing them.

There can be little doubt that during the warm periods of the glacial

epoch our island would be clothed with a luxuriant flora. At the end

of a cold period, when the ice had disappeared, the whole face of the

country would be covered over to a considerable depth with a confused

mass of stones and boulder clay. A surface thus wholly destitute of

every seed and germ would probably remain for years without vegetation.

But through course of time life would begin to appear, and during

the thousands of years of perpetual summer which would follow, the

soil, uncongenial as it no doubt must have been, would be forced to

sustain a luxuriant vegetation. But although this was the case, we

need not wonder that now scarcely a single vestige of it remains; for

when the ice sheet again crept over the island everything animate and

inanimate would be ground down to powder. We are certain that prior

to the glacial epoch our island must have been covered with life and

vegetation. But not a single vestige of these are now to be found;

no, not even of the very soil on which the vegetation grew. The solid

rock itself upon which the soil lay has been ground down to mud by the

ice sheet, and, to a large extent, as Professor Geikie remarks, swept

away into the adjoining seas.[130] It is now even more difficult to

find a trace of the ancient soil _under_ the boulder clay than it is

to find remains of the soil of the warm periods _in_ that clay. As

regards Scotland, cases of old land surfaces under the boulder clay are

as seldom recorded as cases of old land surfaces in it. In so far as

geology is concerned, there is as much evidence to show that our island

was clothed with vegetation during the glacial epoch as there is that

it was so clothed prior to that epoch.

CHAPTER XVI.

WARM INTER-GLACIAL PERIODS IN ARCTIC REGIONS.

Cold Periods best marked in Temperate, and Warm Periods

in Arctic, Regions.—State of Arctic Regions during

Glacial Period.—Effects of Removal of Ice from Arctic

Regions.—Ocean-Currents; Influence on Arctic Climate.—Reason

why Remains of Inter-glacial Period are rare in Arctic

Regions.—Remains of Ancient Forests in Banks’s Land, Prince

Patrick’s Island, &c.—Opinions of Sir R. Murchison, Captain

Osborn, and Professor Haughton.—Tree dug up by Sir E. Belcher

in lat. 75° N.

In the temperate regions the cold periods of the glacial epoch would be

far more marked than the warm inter-glacial periods. The condition of

things which prevailed during the cold periods would differ far more

widely from that which now prevails than would the condition of things

during the warm periods. But as regards the polar regions the reverse

would be the case; there the warm inter-glacial periods would be far

more marked than the cold periods. The condition of things prevailing

in those regions during the warm periods would be in strongest contrast

to what now obtains, but this would not hold true in reference to the

cold periods; for during the latter, matters there would be pretty

much the same as at present, only a good deal more severe. The reason

of this may be seen from what has already been stated in Chapter IV.;

but as it is a point of considerable importance in order to a proper

understanding of the physical state of things prevailing in polar

regions during the glacial epoch, I shall consider this part of the

subject more fully.

During the cold periods, our island, and nearly all places in the

northern temperate regions down to about the same latitude, would be

covered with snow and ice, and all animal and vegetable life within

the glaciated area would to a great extent be destroyed. The presence

of the ice would of itself, for reasons already explained, lower the

mean annual temperature to near the freezing-point. The summers,

notwithstanding the proximity of the sun, would not be warm, on the

contrary their temperature would rise little above the freezing-point.

An excess of evaporation would no doubt take place, owing to the

increase in the intensity of the sun’s rays, but this result would only

tend to increase the snowfall.[131]

During the warm periods our country and the regions under consideration

would experience conditions not differing much from those of the

present, but the climate would probably be somewhat warmer and more

equable. The proximity of the sun during winter would prevent snow

from falling. The summers, owing to the greater distance of the sun,

would probably be somewhat colder than they are now. But the loss of

heat during summer would be to a large extent compensated for by two

causes to which we must here refer. (1.) The much greater amount of

heat conveyed by ocean-currents than at present. (2.) Our summers are

now cooled to a considerable extent by cold aërial currents from the

ice-covered regions of the north. But during the period in question

there would be little or no ice in arctic regions, consequently the

winds would be comparatively warm, whatever direction they came from.

Let us next direct our attention to the state of things in the arctic

regions during the glacial epoch. At present Greenland and other parts

of the arctic regions occupied by land are almost wholly covered

with ice, and as a consequence nearly destitute of vegetable life.

During the cold periods of the glacial epoch the quantity of snow

falling would doubtless be greater and the ice thicker, but as regards

organic life, matters would not probably be much worse than they are

at present. In fact, so far as Greenland and the antarctic continent

are concerned, they are about as destitute of plant life as they can

be. Although an increase in the thickness of the arctic ice would not

greatly alter the present state of matters in those regions, yet what

a transformation would ensue upon the disappearance of the ice! This

would not only raise the summer temperature some twenty degrees or so,

but would afford the necessary conditions for the existence of abundant

animal and plant life. The severity of the climate of Greenland is

due to a very considerable extent, as we have already seen, to the

presence of ice. Get rid of the permanent ice, and the temperature of

the country, _cæteris paribus_, would instantly rise. That Greenland

should ever have enjoyed a temperate climate, capable of supporting

abundant vegetation, has often been matter of astonishment, but this

wonder diminishes when we reflect that during the warm periods it would

be in the arctic regions that the greatest heating effect would take

place, this being due mainly to the transference of nearly all the warm

inter-tropical waters to one hemisphere.

It has been shown in Chapter II. that the heating effects at present

resulting from the transference of heat by ocean-currents increase as

we approach the poles. As a consequence of this it follows that during

the warm periods, when the quantity of warm water transferred would be

nearly doubled, the _increase of heat resulting from this cause would

itself increase_ as the warm pole was approached. This effect, combined

with the shortness of the winter in perihelion and the nearness of the

sun during that season, would prevent the accumulation of snow. During

summer, the sun, it is true, would be at a much greater distance from

the earth than at present, but it must be borne in mind that for a

period of three months the quantity of heat received from the sun at

the north pole would be greater than that received at the equator.

Consequently, after the winter’s snow was melted, this great amount of

heat would go to raise the temperature, and the arctic summer could

not be otherwise than hot. It is not hot at present, but this, be it

observed, is because of the presence of the ice. When we take all these

facts into consideration we need not be surprised that Greenland once

enjoyed a condition of climate totally different from that which now

obtains in that region.

It is, therefore, in the arctic and antarctic regions where we ought

to find the most marked and decided evidence of warm inter-glacial

periods. And doubtless such evidence would be abundantly forthcoming

had these regions not been subjected to such intense denudation since

the glacial epoch, and were so large a portion of the land not still

buried beneath an icy covering, and therefore beyond the geologist’s

reach. Only on islands and such outlying places as are not shrouded in

snow and ice can we hope to meet with any trace of the warm periods of

the glacial epoch: and we may now proceed to consider what relics of

these warm periods have actually been discovered in arctic regions.

_Evidence of Warm Periods in Arctic Regions._—The fact that stumps,

&c., of full-grown trees have been found in places where at present

nothing is to be met with but fields of snow and ice, and where the

mean annual temperature scarcely rises above the zero of the Fahrenheit

thermometer, is good evidence to show that the climate of the arctic

regions was once much warmer than now. The remains of an ancient forest

were discovered by Captain McClure, in Banks’s Land, in latitude 74°

48′. He found a great accumulation of trees, from the sea-level to an

elevation of upwards of 300 feet. “I entered a ravine,” says Captain

McClure, “some miles inland, and found the north side of it, for a

depth of 40 feet from the surface, composed of one mass of wood similar

to what I had before seen.”[132] In the ravine he observed a tree

protruding about 8 feet, and 3 feet in circumference. And he further

states that, “_From the perfect state of the bark_, and the position of

the trees so far from the sea, there can be but little doubt that they

grew originally in the country.” A cone of one of these fir-trees was

brought home, and was found to belong apparently to the genus _Abies_,

resembling _A. (Pinus) alba_.

In Prince Patrick’s Island, in latitude 76° 12′ N., longitude 122°

W., near the head of Walker Inlet, and a considerable distance in the

interior in one of the ravines, a tree protruding about 10 feet from

a bank was discovered by Lieutenant Mecham. It proved to be 4 feet

in circumference. In its neighbourhood several others were seen, all

of them similar to some he had found at Cape Manning; each of them

measured 4 feet round and 30 feet in length. The carpenter stated that

the trees resembled larch. Lieutenant Mecham, from their appearance and

position, concluded that they must have grown in the country.[133]

Trees under similar conditions were also found by Lieutenant Pim on

Prince Patrick’s Island, and by Captain Parry on Melville Island, all

considerably above the present sea-level and at a distance from the

shore. On the coast of New Siberia, Lieutenant Anjou found a cliff of

clay containing stems of trees still capable of being used for fuel.

“This remarkable phenomenon,” says Captain Osborn, “opens a vast field

for conjecture, and the imagination becomes bewildered in trying to

realise that period of the world’s history when the absence of ice and

a milder climate allowed forest trees to grow in a region where now the

ground-willow and dwarf-birch have to struggle for existence.”

Sir Roderick Murchison came to the conclusion that all those trees

were drifted to their present position when the islands of the arctic

archipelago were submerged. But it was the difficulty of accounting

for the growth of trees in such a region which led him to adopt this

hypothesis. His argument is this: “If we imagine,” he says, “that the

timber found in those latitudes grew on the spot we should be driven

to adopt the anomalous hypothesis that, notwithstanding physical

relations of land and water similar to those which now prevail, trees

of large size grew on such _terra firma_ within a few degrees of the

north pole!—a supposition which I consider to be wholly incompatible

with the data in our possession, and at variance with the laws of the

isothermal lines.”[134] This reasoning of Sir Roderick’s may be quite

correct, on the supposition that changes of climate are due to changes

in the distribution of sea and land, as advocated by Sir Charles Lyell.

But these difficulties disappear if we adopt the views advocated in

the foregoing chapters. As Captain Osborn has pointed out, however,

Sir Roderick’s hypothesis leaves the real difficulty untouched. “A

very different climate,” he says, “must then have existed in those

regions to allow driftwood so perfect as to retain its bark to reach

such great distances; and perhaps it may be argued that if that sea was

sufficiently clear of ice to allow such timber to drift unscathed to

Prince Patrick’s Land, that that _very absence of a frozen sea would

allow fir-trees to grow in a soil naturally fertile_.”[135]

As has been already stated, all who have seen those trees in arctic

regions agree in thinking that they grew _in situ_. And Professor

Haughton, in his excellent account of the arctic archipelago appended

to McClintock’s “Narrative of Arctic Discoveries,” after a careful

examination of the entire evidence on the subject, is distinctly of

the same opinion; while the recent researches of Professor Heer put it

beyond doubt that the drift theory must be abandoned.

Undoubtedly the arctic archipelago was submerged to an extent that

could have admitted of those trees being floated to their present

positions. This, as we shall see, follows from theory; but submergence,

without a warmer condition of climate, would not enable trees to reach

those regions with their bark entire.

But in reality we are not left to theorise on the subject, for we

have a well-authenticated case of one of those trees being got by

Captain Belcher standing erect in the position in which it grew. It was

found immediately to the northward of the narrow strait opening into

Wellington Sound, in lat. 75° 32′ N. long. 92° W., and about a mile and

a half inland. The tree was dug up out of the frozen ground, and along

with it a portion of the soil which was immediately in contact with the

roots. The whole was packed in canvas and brought to England. Near to

the spot several knolls of peat mosses about nine inches in depth were

found, containing the bones of the lemming in great numbers. The tree

in question was examined by Sir William Hooker, who gave the following

report concerning it, which bears out strongly the fact of its having

grown _in situ_.

“The piece of wood brought by Sir Edward Belcher from the shores of

Wellington Channel belongs to a species of pine, probably to the _Pinus

(Abies) alba_, the most northern conifer. The structure of the wood

of the specimen brought home differs remarkably in its anatomical

character from that of any other conifer with which I am acquainted.

Each concentric ring (or annual growth) consists of two zones of

tissue; one, the outer, that towards the circumference, is broader, of

a pale colour, and consists of ordinary tubes of fibres of wood, marked

with discs common to all coniferæ. These discs are usually opposite

one another when more than one row of them occur in the direction of

the length of the fibre; and, what is very unusual, present radiating

lines from the central depression to the circumference. Secondly,

the inner zone of each annual ring of wood is narrower, of a dark

colour, and formed of more slender woody fibres, with thicker walls in

proportion to their diameter. These tubes have few or no discs upon

them, but are covered with spiral striæ, giving the appearance of each

tube being formed of a twisted band. The above characters prevail in

all parts of the wood, but are slightly modified in different rings.

Thus the outer zone is broader in some than in others, the disc-bearing

fibres of the outer zone are sometimes faintly marked with spiral

striæ, and the spirally marked fibres of the inner zone sometimes bear

discs. These appearances suggest the annual recurrence of some special

cause that shall thus modify the first and last formed fibres of each

year’s deposit, so that that first formed may differ in amount as

well as in kind from that last formed; and the peculiar conditions of

an arctic climate appear to afford an adequate solution. The inner,

or first-formed zone, must be regarded as imperfectly developed,

being deposited at a season when the functions of the plant are very

intermittently exercised, and when a few short hours of sunshine are

daily succeeded by many of extreme cold. As the season advances the

sun’s heat and light are continuous during the greater part of the

twenty-four hours, and the newly formed wood fibres are hence more

perfectly developed, they are much longer, present no signs of striæ,

but are studded with discs of a more highly organized structure than

are usual in the natural order to which this tree belongs.”[136]

Another circumstance which shows that the tree had grown where it was

found is the fact that in digging up the roots portions of the leaves

were obtained. It may also be mentioned that near this place was found

an old river channel cut deeply into the rock, which, at some remote

period, when the climate must have been less rigorous than at present,

had been occupied by a river of considerable size.

Now, it is evident that if a tree could have grown at Wellington Sound,

there is no reason why one might not have grown at Banks’s Land, or

at Prince Patrick’s Island. And, if the climatic condition of the

country would allow one tree to grow, it would equally as well allow

a hundred, a thousand, or a whole forest. If this, then, be the case,

Sir Roderick’s objection to the theory of growth _in situ_ falls to the

ground.

Another circumstance which favours the idea that those trees grew

during the glacial epoch is the fact that although they are recent,

geologically speaking, and belong to the drift series, yet they are,

historically speaking, very old. The wood, though not fossilized, is so

hardened and changed by age that it will scarcely burn.

CHAPTER XVII.

FORMER GLACIAL EPOCHS.—REASON OF THE IMPERFECTION OF

GEOLOGICAL RECORDS IN REFERENCE TO THEM.

Two Reasons why so little is known of Glacial Epochs.—Evidence

of Glaciation to be found on Land-surfaces.—Where are all

our ancient Land-surfaces?—The stratified Rocks consist

of a Series of old Sea-bottoms.—Transformation of a

Land-surface into a Sea-bottom obliterates all Traces of

Glaciation.—Why so little remains of the Boulder Clays of

former Glacial Epochs.—Records of the Glacial Epoch are fast

disappearing.—Icebergs do not striate the Sea-bottom.—Mr.

Campbell’s Observations on the Coast of Labrador.—Amount

of Material transported by Icebergs much exaggerated.—Mr.

Packard on the Glacial Phenomena of Labrador.—Boulder Clay

the Product of Land-ice.—Palæontological Evidence.—Paucity of

Life characteristic of a Glacial Period.—Warm Periods better

represented by Organic Remains than cold.—Why the Climate

of the Tertiary Period was supposed to be warmer than the

present.—Mr. James Geikie on the Defects of Palæontological

Evidence.—Conclusion.

_Two Reasons why so little is known of former Glacial Epochs._—If the

glacial epoch resulted from the causes discussed in the foregoing

chapters, then such epochs must have frequently supervened. We may,

therefore, now proceed to consider what evidence there is for the

former occurrence of excessive conditions of climate during previous

geological ages. When we begin our inquiry, however, we soon find

that the facts which have been recorded as evidence in favour of the

action of ice in former geological epochs are very scanty indeed. Two

obvious reasons for this may be given, namely, (1) The imperfection

of the geological records themselves, and (2) the little attention

hitherto paid toward researches of this kind. The notion, once so

prevalent, that the climate of our earth was much warmer in the earlier

geological ages than it is now, and that it has ever since been

gradually becoming cooler, was wholly at variance with the idea of

former ice-periods. And this conviction of the _à priori_ improbability

of cold periods having obtained during Palæozoic and Mesozoic ages

tended to prevent due attention being paid to such facts as seemed to

bear upon the subject. But our limited knowledge of former glacial

epochs must no doubt be attributed chiefly to the actual imperfection

of the geological records. So great is this imperfection that the mere

absence of direct geological evidence cannot reasonably be regarded as

sufficient proof that the conclusions derived from astronomical and

physical considerations regarding former ice-periods are improbable.

Nor is this all. The geological records of ancient glacial conditions

are not only imperfect, but, as I shall endeavour to show, this

imperfection _follows as a natural consequence from the principles of

geology itself_. There are not merely so many blanks or gaps in the

records, but a reason exists in the very nature of geological evidence

why such breaks in the record might reasonably be expected to occur.

_Evidence of Glaciation to be found chiefly on Land-surfaces._—It is on

a land-surface that the principal traces of the action of ice during

a glacial epoch are left, for it is there that the stones are chiefly

striated, the rocks ground down, and the boulder clay formed. But where

are all our ancient land-surfaces? They are not to be found. The total

thickness of the stratified rocks of Great Britain is, according to

Professor Ramsay, nearly fourteen miles. But from the top to the bottom

of this enormous pile of deposits there is hardly a single land-surface

to be detected. True patches of old land-surfaces of a local character

exist, such, for example, as the dirt-beds of Portland; but, with the

exception of coal-seams, every general formation from top to bottom

has been accumulated under water, and none but the under-clays _ever

existed as a land_-surface. And it is here, in such a formation,

that the geologist has to collect all his information regarding the

existence of former glacial epochs. The entire stratified rocks of the

globe, with the exception of the coal-beds and under-clays (in neither

of which would one expect to find traces of ice-action), consist almost

entirely of a _series of old sea-bottoms_, with here and there an

occasional freshwater deposit. Bearing this in mind, what is the sort

of evidence which we can now hope to find in these old sea-bottoms of

the existence of former ice-periods?

Every geologist of course admits that the stratified rocks are not

old land-surfaces, but a series of old sea-bottoms formed out of

the accumulated material derived from the degradation of primeval

land-surfaces. And it is true that all land-surfaces once existed

as sea-bottoms; but the stratified rocks consist of a series of old

sea-bottoms which never were land-surfaces. Many of them no doubt

have been repeatedly above the sea-level, and may once have possessed

land-surfaces; but these, with the exception of the under-clays of the

various coal measures, the dirt-beds of Portland, and one or two more

patches, have all been denuded away. The important bearing which this

consideration has on the nature of the evidence which we can now expect

to find of the existence of former glacial epochs has certainly been

very much overlooked.

If we examine the matter fully we shall be led to conclude that the

_transformation of a land-surface into a sea-bottom_ will probably

completely obliterate every trace of glaciation which that land-surface

may once have presented. We cannot, for example, expect to meet with

polished and striated stones belonging to a former land glaciation; for

such stones are not carried down bodily and unchanged by our rivers

and deposited in the sea. They become broken up by subaërial agencies

into gravel, sand, and clay, and in this condition are transported

seawards. Nor even if we supposed it possible that the stones and

boulders derived from a mass of till could be carried down to sea by

river-action, could we at the same time fail to admit that such stones

would be deprived of all their ice-markings, and become water-worn and

rounded on the way.[137]

Nor can we expect to find boulder clay among the stratified rocks, for

boulder clay is not carried down as such and deposited in the sea, but

under the influence of the denuding agents becomes broken up into soft

mud, clay, sand, and gravel, as it is gradually peeled off the land and

swept seawards. Patches of boulder clay may have been now and again

forced into the sea by ice and eventually become covered up; but such

cases are wholly exceptional, and their absence in any formation cannot

fairly be adduced as a proof that that formation does not belong to a

glacial period.

The only evidence of the existence of land-ice during former periods

which we can reasonably expect to meet with in the stratified rocks,

consists of erratic blocks which may have been transported by icebergs

and dropped into the sea. But unless the glaciers of such epochs

reached the sea, we could not possibly possess even this evidence.

Traces in the stratified rocks of the effects of land-ice during former

epochs must, in the very nature of things, be rare indeed. The only

sort of evidence which, as a general rule, we may expect to detect,

is the presence of large erratic blocks imbedded in strata which from

their constitution have evidently been formed in still water. But this

is quite enough; for it proves the existence of ice at the time the

strata were being deposited as conclusively as though we saw the ice

floating with the blocks upon it. This sort of evidence, when found in

low latitudes, ought to be received as conclusive of the existence of

former glacial epochs; and, no doubt, would have been so received had

it not been for the idea that, if these blocks had been transported

by ice, there ought in addition to have been found striated stones,

boulder clay, and other indications of the agency of land-ice.

Of course all erratics are not necessarily transported by masses of

ice broken from the terminal front of glaciers. The “ice foot,” formed

by the freezing of the sea along the coasts of the higher latitudes of

Greenland, carries seawards immense quantities of blocks and _débris_.

And again stones and boulders are frequently frozen into river-ice,

and when the ice breaks up in spring are swept out to sea, and may be

carried some little distance before they are dropped. But both these

cases can occur only in regions where the winters are excessive; nor

is it at all likely that such ice-rafts will succeed in making a long

voyage. If, therefore, we could assure ourselves that the erratics

occasionally met with in certain old geological formations in low

latitudes were really transported from the land by an ice-foot or a

raft of river-ice, we should be forced to conclude that very severe

climatic conditions must have obtained in such latitudes at the time

the erratics were dispersed.

The reason why we now have, comparatively speaking, so little direct

evidence of the existence of former glacial periods will be more

forcibly impressed upon the mind, if we reflect on how difficult it

would be in a million or so of years hence to find any trace of what

we now call the glacial epoch. The striated stones would by that time

be all, or nearly all, disintegrated, and the till washed away and

deposited in the bottom of the sea as stratified sands and clays. And

when these became consolidated into rock and were raised into dry land,

the only evidence that we should probably then have that there ever

had been a glacial epoch would be the presence of large blocks of the

older rocks, which would be found imbedded in the upraised formation.

We could only infer that there had been ice at work from the fact that

by no other known agency could we conceive such blocks to have been

transported and dropped in a still sea.

Probably few geologists believe that during the Middle Eocene and

the Upper Miocene periods our country passed through a condition of

glaciation as severe as it has done during the Post-pliocene period;

yet when we examine the subject carefully, we find that there is

actually no just ground to conclude that it has not. For, in all

probability, throughout the strata to be eventually formed out of the

destruction of the now existing land-surfaces, evidence of ice-action

will be as scarce as in Eocene or Miocene strata.

If the stratified rocks forming the earth’s crust consisted of a series

of old land-surfaces instead (as they actually do) of a series of old

sea-bottoms, then probably traces of many glacial periods might be

detected.

Nearly all the evidence which we have regarding the glacial epoch

has been derived from what we find on the now existing land-surfaces

of the globe. But probably not a vestige of this will exist in the

stratified beds of future ages, formed out of the destruction of the

present land-surfaces. Even the very arctic shell-beds themselves,

which have afforded to the geologist such clear proofs of a frozen sea

during the glacial epoch, will not be found in those stratified rocks;

for they must suffer destruction along with everything else which now

exists above the sea-level. There is probably not a single relic of

the glacial epoch which has ever been seen by the eye of man that will

be treasured up in the stratified rocks of future ages. Nothing that

does not lie buried in the deeper recesses of the ocean will escape

complete disintegration and appear imbedded in those formations. It

is only those objects which lie in our existing sea-bottoms that will

remain as monuments of the glacial epoch of the Post-tertiary period.

And, moreover, it will only be those portions of the sea-bottoms that

may happen to be upraised into dry land that will be available to the

geologist of future ages. The point to be determined now is this:—_Is

it probable that the geologist of the future will find in the rocks

formed out of the now existing sea-bottoms more evidence of a glacial

epoch during Post-tertiary times than we now do of one during, say, the

Miocene, the Eocene, or the Permian period?_ Unless this can be proved

to be the case, we have no ground whatever to conclude that the cold

periods of the Miocene, Eocene, and Permian periods were not as severe

as that of the glacial epoch. This is evident, for the only relics

which now remain of the glacial epochs of those periods are simply

what happened to be protected in the then existing sea-bottoms. Every

vestige that lay on the land would in all probability be destroyed by

subaërial agency and carried into the sea in a sedimentary form. But

before we can determine whether or not there is more evidence of the

glacial epoch in our now existing sea-bottoms than there is of former

glacial epochs in the stratified rocks (which are in reality the

sea-bottoms belonging to ancient epochs), we must first ascertain what

is the nature of those marks of glaciation which are to be found in a

sea-bottom.

_Icebergs do not striate the Sea-bottom._—We know that the rocky face

of the country was ground down and striated during the glacial epoch;

and this is now generally believed to have been done by land-ice. But

we have no direct evidence that the floor of the ocean, beyond where it

may have been covered with land-ice, was striated. Beyond the limits

of the land-ice it could be striated only by means of icebergs. But

do icebergs striate the rocky bed of the ocean? Are they adapted for

such work? It seems to be often assumed that they are. But I have been

totally unable to find any rational grounds for such a belief. Clean

ice can have but little or no erosive power, and never could scratch a

rock. To do this it must have grinding materials in the form of sand,

mud, or stones. But the bottoms of icebergs are devoid of all such

materials. Icebergs carry the grinding materials on their backs, not on

their bottoms. No doubt, when the iceberg is launched into the deep,

great masses of sand, mud, and stones will be adhering to its bottom.

But no sooner is the berg immersed, than a melting process commences

at its sides and lower surface in contact with the water; and the

consequence is, the materials adhering to the lower surface soon drop

off and sink to the bottom of the sea. The iceberg, divested of these

materials, can now do very little harm to the rocky sea-bottom over

which it floats. It is true that an iceberg moving with a velocity

of a few miles an hour, if it came in contact with the sea-bottom,

would, by the mere force of concussion, tear up loose and disjointed

rocks, and hurl some of the loose materials to a distance; but it would

do but little in the way of grinding down the rock against which it

struck. But even supposing the bottom of the iceberg were properly

shod with the necessary grinding materials, still it would be but a

very inefficient grinding agent; for a _floating_ iceberg would not

be in contact with the sea-bottom. And if it were in contact with the

sea-bottom, it would soon become stranded and, of course, motionless,

and under such conditions could produce no effect.

It is perfectly true that although the bottom of the berg may be devoid

of grinding materials, yet these may be found lying on the surface

of the submarine rock over which the ice moves. But it must be borne

in mind that the same current which will move the icebergs over the

surface of the rock will move the sand, mud, and other materials

over it also; so that the markings effected by the ice would in all

probability be erased by the current. In the deep recesses of the

ocean the water has been found to have but little or no motion. But

icebergs always follow the path of currents; and it is very evident

that at the comparatively small depth of a thousand feet or so reached

by icebergs the motion of the water will be considerable; and the

continual shifting of the small particles of the mud and sand will in

all probability efface the markings which may be made now and again by

a passing berg.

Much has been said regarding the superiority of icebergs as grinding

and striating agents in consequence of the great velocity of their

motion in comparison with that of land-ice. But it must be remembered

that it is while the iceberg is floating, and before it touches the

rock, that it possesses high velocity. When the iceberg runs aground,

its motion is suddenly arrested or greatly reduced. But if the iceberg

advancing upon a sloping sea-bottom is raised up so as to exert great

pressure, it will on this account be the more suddenly arrested,

the motion will be slow, and the distance passed over short, before

the berg becomes stranded. If it exerts but little pressure on the

sea-bottom, it may retain a considerable amount of motion and advance

to a considerable distance before it is brought to a stand; but,

exerting little pressure, it can perform but little work. Land-ice

moves slowly, but then it exerts enormous pressure. A glacier 1,000

feet in thickness has a pressure on its rocky bed equal to about 25

tons on the square foot; but an iceberg a mile in thickness, forced up

on a sloping sea-bottom to an elevation of 20 feet (and this is perhaps

more than any ocean-current could effect), would only exert a pressure

of about half a ton on the square foot, or about 1/50th part of the

pressure of the glacier 1,000 feet in thickness. A great deal has been

said about the erosive and crushing power of icebergs of enormous

thickness, as if their thickness gave them any additional pressure. An

iceberg 100 feet in thickness will exert just as much pressure as one

a mile in thickness. The pressure of an iceberg is not like that of a

glacier, in proportion to its thickness, but to the height to which it

is raised out of the water. An iceberg 100 feet in thickness raised 10

feet will exert exactly the same pressure as one a mile in thickness

raised to an equal height.

To be an efficient grinding agent, steadiness of motion, as well as

pressure, is essential. A rolling or rocking motion is ill-adapted

for grinding down and striating a rock. A steady rubbing motion under

pressure is the thing required. But an iceberg is not only deficient in

pressure, but also deficient in steadiness of motion. When an iceberg

moving with considerable velocity comes on an elevated portion of the

sea-bottom, it does not move steadily onwards over the rock, unless

the pressure of the berg on the rock be trifling. The resistance being

entirely at the bottom of the iceberg, its momentum, combined with the

pressure of the current, applied wholly above the point of resistance,

tends to make the berg bend forward, and in some cases upset (when

it is of a cubical form). The momentum of the moving berg, instead

of being applied in forcing it over the rock against which it comes

in contact, is probably all consumed in work against gravitation in

raising the berg upon its front edge. After the momentum is consumed,

unless the berg be completely upset, it will fall back under the force

of gravitation to its original position. But the momentum which it

acquires from gravitation in falling backwards carries it beyond its

position of repose in an opposite direction. It will thus continue to

rock backwards and forwards until the friction of the water brings it

to rest. The momentum of the berg, instead of being applied to the work

of grinding and striating the sea-bottom, will chiefly be consumed in

heat in the agitation of the water. But if the berg does advance, it

will do so with a rocking unsteady motion, which, as Mr. Couthouy[138]

and Professor Dana[139] observe, will tend rather to obliterate

striations than produce them.

A floating berg moves with great steadiness; but a berg that has run

aground cannot advance with a steady motion. If the rock over which the

berg moves offers little resistance, it may do so; but in such a case

the berg could produce but little effect on the rock.

Dr. Sutherland, who has had good opportunities to witness the effects

of icebergs, makes some most judicious remarks on the subject. “It

will be well” he says, “to bear in mind that when an iceberg _touches

the ground, if that ground be hard and resisting, it must come to a

stand_, and the propelling power continuing, a slight leaning over in

the water, or yielding motion of the whole mass, may compensate readily

for being so suddenly arrested. If, however, the ground be soft, so

as not to arrest the motion of the iceberg at once, a moraine will be

the result; but the moraine thus raised will tend to bring it to a

stand.”[140]

There is another cause referred to by Professor Dana, which, to a

great extent, must prevent the iceberg from having an opportunity of

striating the sea-bottom, even though it were otherwise well adapted

for so doing. It is this: the bed of the ocean in the track of

icebergs must be pretty much covered with stones and rubbish dropped

from the melting bergs. And this mass of rubbish will tend to protect

the rock.[141]

If icebergs cannot be shown _à priori_, from mechanical considerations,

to be well adapted for striating the sea-bottom, one would naturally

expect, from the confident way in which it is asserted that they are

so adapted, that the fact has been at least established by actual

observation. But, strange as it may appear, we seem to have little or

no proof that icebergs actually striate the bed of the ocean. This can

be proved from the direct testimony of the advocates of the iceberg

theory themselves.

We shall take the testimony of Mr. Campbell, the author of two

well-known works in defence of the iceberg theory, viz., “Frost and

Fire,” and “A Short American Tramp.” Mr. Campbell went in the fall of

the year 1864 to the coast of Labrador, the Straits of Belle Isle, and

the Gulf of St. Lawrence, for the express purpose of witnessing the

effects of icebergs, and testing the theory which he had formed, that

the ice-markings of the glacial epoch were caused by floating ice and

not by land-ice, as is now generally believed.

The following is the result of his observations on the coast of

Labrador.

Hanly Harbour, Strait of Belle Isle:—“The water is 37° F. in July....

As fast as one island of ice grounds and bursts, another takes its

place; and in winter the whole strait is blocked up by a mass which

swings bodily up and down, grating along the bottom at all depths....

Examined the beaches and rocks at the water-line, especially in sounds.

Found the rocks ground smooth, _but not striated_, in the sounds”

(_Short American Tramp_, pp. 68, 107).

Cape Charles and Battle Harbour:—“But though these harbours are all

frozen every winter, the _rocks at the water-line are not striated_”

(p. 68).

At St. Francis Harbour:—“The water-line is much rubbed, smooth, _but

not striated_” (p. 72).

Cape Bluff:—“Watched the rocks with a telescope, and _failed to make

out striæ anywhere_; but the water-line is everywhere rubbed smooth”

(p. 75).

Seal Islands:—“_No striæ are to be seen at the land-wash in these

sounds or on open sea-coasts near the present water-line_” (p. 76).

He only mentions having here found striations in the three following

places along the entire coast of Labrador visited by him; and in regard

to two of these, it seems very doubtful that the markings were made by

modern icebergs.

Murray’s Harbour:—“This harbour was blocked up with ice on the 20th of

July. The water-line is rubbed, and in _some places_ striated” (p. 69).

Pack Island:—“The water-line in a narrow sound was polished and

striated in the direction of the sound, about N.N.W. This seems to be

fresh work done by heavy ice drifting from Sandwich Bay; _but, on the

other hand, stages with their legs in the sea, and resting on these

very rocks, are not swept away by the ice_” (p. 96). If these markings

were modern, why did not the “heavy ice” remove the small fir poles

supporting the fishing-stages?

Red Bay:—“Landed half-dressed, and found some striæ perfectly fresh at

the water-level, but weathered out a short distance _inland_” (p. 107).

The striations “inland” could not have been made by modern icebergs;

and it does not follow that because the markings at the water-level

were not weathered they were produced by modern ice.

These are the evidences which he found that icebergs striate rocks,

on a coast of which he says that, during the year he visited it, “the

winter-drift was one vast solid raft of floes and bergs more than 150

miles wide, and perhaps 3,000 feet thick at spots, driven by a whole

current bodily over one definite course, year after year, since this

land was found” (p. 85).

But Mr. Campbell himself freely admits that the floating ice which

comes aground along the shores does not produce striæ. “It is

sufficiently evident,” he says, “_that glacial striæ are not produced

by thin bay-ice_” (p. 76). And in “Frost and Fire,” vol. ii., p. 237,

he states that, “from a careful examination of the water-line at many

spots, it appears that bay-ice grinds rocks, _but does not produce

striation_.”

“It is impossible,” he continues, “to get at rocks over which heavy

icebergs now move; but a mass 150 miles wide, perhaps 3,000 feet thick

in some parts, and moving at the rate of a mile an hour, or more,

_appears to be an engine amply sufficient_ to account for striæ on

rising rocks.” And in “American Tramp,” p. 76, he says, “_striæ must be

made_ in deep water by the large masses which seem to pursue the even

tenor of their way in the steady current which flows down the coast.”

Mr. Campbell, from a careful examination of the sea-bottom along the

coast, finds that the small icebergs do not produce striæ, but the

large ones, which move over rocks impossible to be got at, “must”

produce them. They “appear” to be amply sufficient to do so. If the

smaller bergs cannot striate the sea-bottom, why must the larger ones

do so? There is no reason why the smaller bergs should not move as

swiftly and exert as much pressure on the sea-bottom as the larger

ones. And even supposing that they did not, one would expect that the

light bergs would effect on a smaller scale what the heavy ones would

do on a larger.

I have no doubt that when Mr. Campbell visited Labrador he expected to

find the sea-coast under the water-line striated by means of icebergs,

and was probably not a little surprised to find that it actually was

not. And I have no doubt that were the sea-bottom in the tracks of the

large icebergs elevated into view, he would find to his surprise that

it was free from striations also.

So far as observation is concerned, we have no grounds from what Mr.

Campbell witnessed to conclude that icebergs striate the sea-bottom.

The testimony of Dr. Sutherland, who has had opportunities of seeing

the effects of icebergs in arctic regions, leads us to the same

conclusion. “Except,” he says, “from the evidence afforded by plants

and animals at the bottom, we have _no means whatever_ to ascertain

the effect produced by icebergs upon the rocks.[142] In the Malegat

and Waigat I have seen whole clusters of these floating islands,

drawing from 100 to 250 fathoms, moving to and fro with every return

and recession of the tides. I looked very earnestly for grooves and

scratches left by icebergs and glaciers in the rocks, but always failed

to discover any.”[143]

We shall now see whether river-ice actually produces striations or not.

If floating ice under any form can striate rocks, one would expect that

it ought to be done by river-ice, seeing that such ice is obliged to

follow one narrow definite track.

St. John’s River, New Brunswick:—“This river,” says Mr. Campbell,

“is obstructed by ice during five months of the year. When the ice

goes, there is wild work on the bank. Arrived at St. John, drove

to the suspension-bridge.... At this spot, if _anywhere in the

world_, river-ice ought to produce striation. The whole drainage of

a wide basin and one of the strongest tides in the world, here work

continually in one rock-groove; and in winter this water-power is armed

with heavy ice. _There are no striæ_ about the water-line.”[144]

River St. Lawrence:—“In winter the power of ice-floats driven by

water-power is tremendous. The river freezes and packs ice till the

flow of water is obstructed. The rock-pass at Quebec is like the

Narrows at St. John’s, Newfoundland. The whole pass, about a mile

wide, was paved with great broken slabs and round boulders of worn ice

as big as small shacks, piled and tossed, and heaped and scattered

upon the level water below and frozen solid.... This kind of ice does

NOT _produce striation_ at the water-margin at Quebec. At Montreal,

when the river ‘goes,’ the ice goes with it with a vengeance.... The

_piers are not yet striated_ by river-ice at Montreal.... The rocks

at the high-water level have _no trace_ of glacial striæ.... The rock

at Ottawa is rubbed by river-ice every spring, and _always in one

direction, but it is not striated_.... The surfaces are all rubbed

smooth, and the edges of broken beds are rounded where exposed to the

ice; _but there are no striæ_.”[145]

When Sir Charles Lyell visited the St. Lawrence in 1842, at Quebec he

went along with Colonel Codrington “and searched carefully below the

city in the channel of the St. Lawrence, at low water, near the shore,

for the signs of glacial action at the precise point where the chief

pressure and friction of packed ice are exerted every year,” but found

none.

“At the bridge above the Falls of Montmorenci, over which a large

quantity of ice passes every year, the gneiss is polished, and kept

perfectly free from lichens, but not more so than rocks similarly

situated at waterfalls in Scotland. In none of these places were any

long straight grooves observable.”[146]

The only thing in the shape of modern ice-markings which he seems to

have met with in North America was a few straight furrows half an inch

broad in soft sandstone, at the base of a cliff at Cape Blomidon in the

Bay of Fundy, at a place where during the preceding winter “packed”

ice 15 feet thick had been pushed along when the tide rose over the

sandstone ledges.[147]

The very fact that a geologist so eminent as Sir Charles Lyell, after

having twice visited North America, and searched specially for modern

ice-markings, was able to find only two or three scratches, upon a soft

sandstone rock, which he could reasonably attribute to floating ice,

ought to have aroused the suspicion of the advocates of the iceberg

theory that they had really formed too extravagant notions regarding

the potency of floating ice as a striating agent.

There is no reason to believe that the grooves and markings noticed

by M. Weibye and others on the Scandinavian coast and other parts of

northern Europe were made by icebergs.

Professor Geikie has clearly shown, from the character and direction

of the markings, that they are the production of land-ice.[148] If

the floating ice of the St. Lawrence and the icebergs of Labrador are

unable to striate and groove the rocks, it is not likely that those of

northern Europe will be able to do so.

It will not do for the advocates of the iceberg theory to assume, as

they have hitherto done, that, as a matter of course, the sea-bottom is

being striated and grooved by means of icebergs. They must prove that.

They must either show that, as a matter of fact, icebergs are actually

efficient agents in striating the sea-bottom, or prove from mechanical

principles that they must be so. The question must be settled either by

observation or by reason; mere opinion will not do.

_The Amount of Material transported by Icebergs much exaggerated._—The

transporting of boulders and rubbish, and not the grinding and

striating of rocks, is evidently the proper function of the iceberg.

But even in this respect I fear too much has been attributed to it.

In reading the details of voyages in the arctic regions one cannot help

feeling surprised how seldom reference is made to stones and rubbish

being seen on icebergs. Arctic voyagers, like other people, when they

are alluding to the geological effects of icebergs, speak of enormous

quantities of stones being transported by them; but in reading the

details of their voyages, the impression conveyed is that icebergs with

stones and blocks of rock upon them are the exceptions. The greater

portion of the narratives of voyages in arctic regions consists of

interesting and detailed accounts of the voyager’s adventures among the

ice. The general appearance of the icebergs, their shape, their size,

their height, their colour, are all noticed; but rarely is mention

made of stones being seen. That the greater number of icebergs have

no stones or rubbish on them is borne out by the positive evidence of

geologists who have had opportunities of seeing icebergs.

Mr. Campbell says:—“It is remarkable that up to this time we have only

seen a few doubtful stones on bergs which we have passed.... Though

no bergs with stones _on them or in them_ have been approached during

this voyage, many on board the _Ariel_ have been close to bergs heavily

laden.... A man who has had some experience of ice has _never seen a

stone on a berg_ in these latitudes. Captain Anderson, of the _Europa_,

who is a geologist, has _never seen a stone on a berg_ in crossing the

Atlantic. _No stones were clearly seen on this trip._”[149] Captain Sir

James Anderson (who has long been familiar with geology, has spent a

considerable part of his life on the Atlantic, and has been accustomed

to view the iceberg as a geologist as well as a seaman) has never seen

a stone on an iceberg in the Atlantic. This is rather a significant

fact.

Sir Charles Lyell states that, when passing icebergs on the Atlantic,

he “was most anxious to ascertain whether there was any mud, stones,

or fragments of rocks on any one of these floating masses; but after

examining about forty of them without perceiving any signs of frozen

matter, I left the deck when it was growing dusk.”[150] After he had

gone below, one was said to be seen with something like stones upon it.

The captain and officers of the ship assured him that they had _never

seen a stone upon a berg_.

The following extract from Mr. Packard’s “Memoir on the Glacial

Phenomena of Labrador and Maine,” will show how little is effected by

the great masses of floating ice on the Labrador coast either in the

way of grinding and striating the rocks, or of transporting stones,

clay, and other materials.

“Upon this coast, which during the summer of 1864 was lined with a

belt of floe-ice and bergs probably two hundred miles broad, and which

extended from the Gulf of St. Lawrence at Belles Amours to the arctic

seas, this immense body of floating ice seemed _directly_ to produce

but little alteration in its physical features. If we were to ascribe

the grooving and polishing of rocks to the action of floating ice-floes

and bergs, how is it that the present shores far above (500), and at

least 250 feet below, the water-line are often jagged and angular,

though constantly stopping the course of masses of ice impelled four to

six miles an hour by the joint action of tides, currents, and winds? No

boulders, or gravel, or mud were seen upon any of the bergs or masses

of shore-ice. They had dropped all burdens of this nature nearer their

points of detachment in the high arctic regions.” ...

“This huge area of floating ice, embracing so many thousands of square

miles, was of greater extent, and remained longer upon the coast, in

1864, than for forty years previous. It was not only pressed upon the

coast by the normal action of the Labrador and Greenland currents,

which, in consequence of the rotatory motion of the earth, tended to

force the ice in a south-westerly direction, but the presence of the

ice caused the constant passage of cooler currents of air from the

sea over the ice upon the heated land, giving rise during the present

season to a constant succession of north-easterly winds from March

until early in August, which further served to crowd the ice into every

harbour and recess upon the coast. It was the universal complaint

of the inhabitants that the easterly winds were more prevalent, and

the ice ‘held’ later in the harbours this year than for many seasons

previous. Thus the fisheries were nearly a failure, and vegetation

greatly retarded in its development. But so far as polishing and

striating the rocks, depositing drift material, and thus modifying

the contour of the surface of the present coast, this modern mass of

bergs and floating ice effected comparatively little. Single icebergs,

when small enough, entered the harbours, and there stranding, soon

pounded to pieces upon the rocks, melted, and disappeared. From Cape

Harrison, in lat. 55°, to Caribo Island, was an interrupted line of

bergs stranded in 80 to 100 or more fathoms, often miles apart, while

others passed to the seaward down by the eastern coast of Newfoundland,

or through the Straits of Belle Isle.”[151]

_Boulder Clay the Product of Land-ice._—There is still another point

connected with icebergs to which we must allude, viz., the opinion

that great masses of the boulder clay of the glacial epoch were formed

from the droppings of icebergs. If boulder clay is at present being

accumulated in this manner, then traces of the boulder clay deposits of

former epochs might be expected to occur. It is perfectly obvious that

_unstratified_ boulder clay could not have been formed in this way.

Stones, gravel, sand, clay, and mud, the ingredients of boulder clay,

tumbled all together from the back of an iceberg, could not sink to the

bottom of the sea without separating. The stones would reach the bottom

first, then the gravel, then the sand, then the clay, and last of all

the mud, and the whole would settle down in a stratified form. But,

besides, how could the _clay_ be derived from icebergs? Icebergs derive

their materials from the land before they are launched into the deep,

and while they are in the form of land-ice. The materials which are

found on the backs of icebergs are what fell upon the ice from mountain

tops and crags projecting above the ice. Icebergs are chiefly derived

from continental ice, such as that of Greenland, where the whole

country is buried under one continuous mass, with only a lofty mountain

peak here and there rising above the surface. And this is no doubt

the chief reason why so few icebergs have stones upon their backs.

The continental ice of Greenland is not, like the glaciers of the

Alps, covered with loose stones. Dr. Robert Brown informs me that no

moraine matter has ever been seen on the inland ice of Greenland. It is

perfectly plain that clay does not fall upon the ice. What falls upon

the ice is stones, blocks of rocks, and the loose _débris_. Clay and

mud we know, from the accounts given by arctic voyagers, are sometimes

washed down upon the coast-ice; but certainly very little of either can

possibly get upon an iceberg. Arctic voyagers sometimes speak of seeing

clay and mud upon bergs; but it is probable that if they had been near

enough they would have found that what they took for clay and mud were

merely dust and rubbish.

Undoubtedly the boulder clay of many places bears unmistakable evidence

of having been formed under water; but it does not on that account

follow that it was formed from the droppings of icebergs. The fact

that the boulder clay in every case _is chiefly composed of materials

derived from the country on which the clay lies_, proves that it was

not formed from matter transported by icebergs. The clay, no doubt,

contains stones and boulders belonging to other countries, which in

some cases may have been transported by icebergs; but the clay itself

has not come from another country. But if the clay itself has been

derived from the country on which it lies, then it is absurd to suppose

that it was deposited from icebergs. The clay and materials which are

found on icebergs are derived from the land on which the iceberg is

formed; but to suppose that icebergs, after floating about upon the

ocean, should always return to the country which gave them birth, and

there deposit their loads, is rather an extravagant supposition.

From the facts and considerations adduced we are, I would venture to

presume, warranted to conclude that, with the exception of what may

have been produced by land-ice, very little in the shape of boulder

clay or striated rocks belonging to the glacial epoch lies buried

under the ocean—and that when the now existing land-surfaces are all

denuded, probably scarcely a trace of the glacial epoch will then be

found, except the huge blocks that were transported by icebergs and

dropped into the sea. It is therefore probable that we have as much

evidence of the existence of a glacial epoch during former periods as

the geologists of future ages will have of the existence of a glacial

epoch during the Post-tertiary period, and that consequently we are not

warranted in concluding that the glacial epoch was something unique in

the geological history of our globe.

_Palæontological Evidence._—It might be thought that if glacial epochs

have been numerous, we ought to have abundance of palæontological

evidence of their existence. I do not know if this necessarily follows.

Let us take the glacial epoch itself for example, which is quite a

modern affair. Here we do not require to go and search in the bottom

of the sea for the evidence of its existence; for we have the surface

of the land in almost identically the same state in which it was when

the ice left it, with the boulder clay and all the wreck of the ice

lying upon it. But what geologist, with all these materials before him,

would be able to find out from palæontological evidence alone that

there had been such an epoch? He might search the whole, but would not

be able to find fossil evidence from which he could warrantably infer

that the country had ever been covered with ice. We have evidence

in the fossils of the Crag and other deposits of the existence of a

colder condition of climate prior to the true glacial period, and in

the shell-beds of the Clyde and other places of a similar state of

matters after the great ice-sheets had vanished away. But in regard

to the period of the true boulder clay or till, when the country was

enveloped in ice, palæontology has almost nothing whatever to tell

us. “Whatever may be the cause,” says Sir Charles Lyell, “the fact is

certain that over large areas in Scotland, Ireland, and Wales, I might

add throughout the northern hemisphere on both sides of the Atlantic,

the stratified drift of the glacial period is very commonly devoid of

fossils.”[152]

In the “flysch” of the Eocene of the Alps, to which we shall have

occasion to refer in the next chapter, in which the huge blocks are

found which prove the existence of ice-action during that period, few

or no fossils have been found. So devoid of organic remains is that

formation, that it is only from its position, says Sir Charles, that

it is known to belong to the middle or “nummulitic” portion of the

great Eocene series. Again, in the conglomerates at Turin, belonging

to the Upper Miocene period, in which the angular blocks of limestone

are found which prove that during that period Alpine glaciers reached

the sea-level in the latitude of Italy, not a single organic remain has

been found. It would seem that an extreme paucity of organic life is a

characteristic of a glacial period, which warrants us in concluding

that the absence of organic remains in any formation otherwise

indicative of a cold climate cannot be regarded as sufficient evidence

that that formation does not belong to a cold period.

In the last chapter it was shown why so little evidence of the warm

periods of the glacial epoch is now forthcoming. The remains of the

_faunas_ and _floras_ of those periods were nearly wholly destroyed and

swept into the adjoining seas by the ice-sheet that covered the land.

It is upon the present land-surface that we find the chief evidence

of the last glacial epoch, but the traces of the warm periods of that

epoch are hardly now to be met with in that position since they have

nearly all been obliterated or carried into the sea.

In regard to former glacial epochs, however, ice-marked rocks,

scratched stones, moraines, till, &c., no longer exist; the

land-surfaces of those old times have been utterly swept away. The only

evidence, therefore, of such ancient glacial epochs, that we can hope

to detect, must be sought for in the deposits that were laid down upon

the sea-bottom; where also we may expect to find traces of the warm

periods that alternated during such epochs with glacial conditions. It

is plain, moreover, that the palæontological evidence in favour of warm

periods will always be the most abundant and satisfactory.

Judging from geological evidence alone, we naturally conclude that, as

a general rule, the climate of former periods was somewhat warmer than

it is at the present day. It is from fossil remains that the geologist

principally forms his estimate of the character of the climate during

any period. Now, in regard to fossil remains, the warm periods will

always be far better represented than the cold; for we find that, as

a _general rule, those formations which geologists are inclined to

believe indicate a cold condition of climate are remarkably devoid of

fossil remains_. If a geologist does not keep this principle in view,

he will be very apt to form a wrong estimate of the general character

of the climate of a period of such enormous length as say the Tertiary.

Suppose that the presently existing sea-bottoms, which have been

forming since the commencement of the glacial epoch, were to become

consolidated into rock and thereafter to be elevated into dry land, we

should then have a formation which might be properly designated the

Post-pliocene. It would represent the time which has elapsed from the

beginning of the glacial epoch to the present day. Suppose one to be

called upon as a geologist to determine from that formation what was

the general character of the climate during the period in question,

what would probably be the conclusion at which he would arrive? He

would probably find here and there patches of boulder clay containing

striated and ice-worn stones. Now and again he would meet with bones

of the mammoth and the reindeer, and shells of an arctic type. He

would likewise stumble upon huge blocks of the older rocks imbedded

in the formation, from which he would infer the existence of icebergs

and glaciers reaching the sea-level. But, on the whole, he would

perceive that the greater portion of the fossil remains met with in

this formation implied a warm and temperate condition of climate. At

the lower part of the formation, corresponding to the time of the true

boulder clay, there would be such a scarcity of organic remains that

he would probably feel at a loss to say whether the climate at that

time was cold or hot. But if the intense cold of the glacial epoch

was not continuous, but broken up by intervening warm periods during

which the ice, to a considerable extent at least, disappeared for a

long period of time (and there are few geologists who have properly

studied the subject who will positively deny that such was the case),

then the country would no doubt during those warm periods possess an

abundance of plant and animal life. It is quite true that we may almost

search in vain on the present land-surface for the organic remains

which belonged to those inter-glacial periods; for they were nearly

all swept away by the ice which followed. But no doubt in the deep

recesses of the ocean, buried under hundreds of feet of sand, mud,

clay, and gravel, lie multitudes of the plants and animals which then

flourished on the land, and were carried down by rivers into the sea.

And along with these lie the skeletons, shells, and other exuviæ of

the creatures which flourished in the warm seas of those periods. Now

looking at the great abundance of fossils indicative of warm and genial

conditions which the lower portions of this formation would contain,

the geologist might be in danger of inferring that the earlier part

of the Post-pliocene period was a warmer period, whereas we, at the

present day, looking at the matter from a different standpoint, declare

that part to have been characterized by cold or glacial conditions. No

doubt, if the beds formed during the cold periods of the glacial epoch

could be distinguished from those formed during the warm periods, the

fossil remains of the one would indicate a cold condition of climate,

and those of the other a warm condition; but still, taking the entire

epoch as a whole, the percentage of fossil remains indicative of a

warm condition would probably so much exceed that indicative of a cold

condition, that we should come to the conclusion that the character

of the climate, as a whole, during the epoch in question was warm and

equable.

As geologists we have, as a rule, no means of arriving at a knowledge

of the character of the climate of any given period but through an

examination of the sea-bottoms belonging to that period; for these

contain all the evidence upon the subject. But unless we exercise

caution, we shall be very apt, in judging of the climate of such

a period, to fall into the same error that we have just now seen

one might naturally fall into were he called upon to determine the

character of the climate during the glacial epoch from the nature of

the organic remains which lie buried in our adjoining seas. On this

point Mr. J. Geikie’s observations are so appropriate, that I cannot

do better than introduce them here. “When we are dealing,” says this

writer, “with formations so far removed from us in time, and in which

the animal and plant remains depart so widely from existing forms of

life, we can hardly expect to derive much aid from the fossils in our

attempts to detect traces of cold climatic conditions. The arctic

shells in our Post-tertiary clays are convincing proofs of the former

existence in our latitude of a severe climate; but when we go so far

back as Palæozoic ages, we have no such clear evidence to guide us.

All that palæontologists can say regarding the fossils belonging to

these old times is simply this, that they seem to indicate, generally

speaking, mild, temperate, or genial, and even sometimes tropical,

conditions of climate. Many of the fossils, indeed, if we are to reason

from analogy at all, could not possibly have lived in cold seas. But,

for aught that we know, there may have been alternations of climate

during the deposition of each particular formation; and these changes

may be marked by the presence or absence, or by the greater or less

abundant development, of certain organisms at various horizons in

the strata. Notwithstanding all that has been done, our knowledge of

the natural history of these ancient seas is still very imperfect;

and therefore, in the present state of our information, we are not

entitled to argue, from the general aspect of the fossils in our older

formations, that the temperature of the ancient seas was never other

than mild and genial.”[153]

_Conclusion._—From what has already been stated it will, I trust, be

apparent that, assuming glacial epochs during past geological ages to

have been as numerous and as severe as the Secular theory demands,

still it would be unreasonable to expect to meet with abundant traces

of them. The imperfection of the geological record is such that we

ought not to be astonished that so few relics of former ice ages have

come down to us. It will also be apparent that the palæontological

evidence of a warm condition of climate having obtained during any

particular age, is no proof that a glacial epoch did not also supervene

during the same cycle of time. Indeed it is quite the reverse; for

the warm conditions of which we have proof may indicate merely the

existence of an inter-glacial period. Furthermore, if the Secular

theory of changes of climate be admitted, then evidence of a warm

condition of climate having prevailed in arctic regions during any

past geological age may be regarded as presumptive proof of the

existence of a glacial epoch; that is to say, of an epoch during

which cold and warm conditions of climate alternated. Keeping these

considerations in view, we shall now proceed to examine briefly what

evidence we at present have of the former existence of glacial epochs.

CHAPTER XVIII.

FORMER GLACIAL EPOCHS; GEOLOGICAL EVIDENCE OF.

Cambrian Conglomerate of Islay and North-west of

Scotland.—Ice-action in Ayrshire and Wigtownshire

during Silurian Period.—Silurian Limestones in Arctic

Regions.—Professor Ramsay on Ice-action during Old

Red Sandstone Period.—Warm Climate in Arctic Regions

during Old Red Sandstone Period.—Professor Geikie and

Mr. James Geikie on a Glacial Conglomerate of Lower

Carboniferous Age.—Professor Haughton and Professor Dawson

on Evidence of Ice-action during Coal Period.—Mr. W. T.

Blanford on Glaciation in India during Carboniferous

Period.—Carboniferous Formations of Arctic Regions.—Professor

Ramsay on Permian Glaciers.—Permian Conglomerate in

Arran.—Professor Hull on Boulder Clay of Permian Age.—Permian

Boulder Clay of Natal.—Oolitic Boulder Conglomerate in

Sutherlandshire.—Warm Climate in North Greenland during

Oolitic Period.—Mr. Godwin-Austen on Ice-action during

Cretaceous Period.—Glacial Conglomerates of Eocene Age in the

Alps.—M. Gastaldi on the Ice-transported Limestone Blocks of

the Superga.—Professor Heer on the Climate of North Greenland

during Miocene Period.

CAMBRIAN PERIOD.

_Island of Islay._—Good evidence of ice-action has been observed by

Mr. James Thomson, F.G.S.,[154] in strata which he believes to be of

Cambrian age. At Port Askaig, Island of Islay, below a precipitous

cliff of quartzite 70 feet in height, there is a mass of arenaceous

talcose schist containing fragments of granite, some angular, but

most of them rounded, and of all sizes, from mere particles to

large boulders. As there is no granite in the island from which

these boulders could have been derived, he justly infers that they

must have been transported by the agency of ice. The probability

of his conclusion is strengthened by the almost total absence of

stratification in the deposit in question.

_North-west of Scotland._—Mr. J. Geikie tells me that much of the

Cambrian conglomerate in the north-west of Scotland strongly reminds

him of the coarse shingle beds (Alpine diluvium) which so often crowd

the old glacial valleys of Switzerland and Northern Italy. In many

places the stones of the Cambrian conglomerate have a subangular,

blunted shape, like those of the re-arranged moraine débris of Alpine

countries.

SILURIAN PERIOD.

_Wigtownshire._—The possibility of glacial action so far back as

the Silurian age has been suggested. In beds of slate and shales in

Wigtownshire of Lower Silurian age Mr. J. Carrick Moore found beds of

conglomerate of a remarkable character. The fragments generally vary

from the size of one inch to a foot in diameter, but in some of the

beds, boulders of 3, 4, and even 5 feet in diameter occur. There are

no rocks in the neighbourhood from which any of these fragments could

have been derived. The matrix of this conglomerate is sometimes a green

trappean-looking sandstone of exceeding toughness, and sometimes an

indurated sandstone indistinguishable from many common varieties of

greywacke.[155]

_Ayrshire._—Mr. James Geikie states that in Glenapp, and near

Dalmellington, he found embedded in Lower Silurian strata blocks

and boulders from one foot to 5 feet in diameter of gneiss,

syenite, granite, &c., none of which belong to rocks of those

neighbourhoods.[156] Similar cases have been found in Galway, Ireland,

and at Lisbellaw, south of Enniskillen.[157] In America, Professor

Dawson describes Silurian conglomerates with boulders 2 feet in

diameter.

_Arctic Regions._—The existence of warm inter-glacial periods

during that age may be inferred from the fact that in the arctic

regions we find widespread masses of Silurian limestones containing

encrinites, corals, and mollusca, and other fossil remains, for an

account of which see Professor Haughton’s geological account of the

Arctic Archipelago appended to McClintock’s “Narrative of Arctic

Discoveries.”[158]

OLD RED SANDSTONE.

_North of England._—According to Professor Ramsay and some other

geologists the brecciated, subangular conglomerates and boulder beds

of the Old Red Sandstone of Scotland and the North of England are of

glacial origin. When these conglomerates and the recent boulder clay

come together it is difficult to draw the line of demarcation between

them.

Professor Ramsay observed some very remarkable facts in connection

with the Old Red Sandstone conglomerates of Kirkby Lonsdale, and

Sedburgh, in Westmoreland and Yorkshire. I shall give the results of

his observations in his own words.

“The result is, that we have found many stones and blocks distinctly

scratched, and on others the ghosts of scratches nearly obliterated

by age and chemical action, probably aided by pressure at a time when

these rocks were buried under thousands of feet of carboniferous

strata. In some cases, however, the markings were probably produced

within the body of the rock itself by pressure, accompanied by

disturbance of the strata; but in others the longitudinal and cross

striations convey the idea of glacial action. The shapes of the stones

of these conglomerates, many of which are from 2 to 3 feet long, their

flattened sides and subangular edges, together with the confused manner

in which they are often arranged (like stones in the drift), have

long been enough to convince me of their ice-borne character; and the

scratched specimens, when properly investigated, may possibly convince

others.”[159]

_Isle of Man._—The conglomerate of the Old Red Sandstone in the Isle of

Man has been compared by Mr. Cumming to “a consolidated ancient boulder

clay.” And he remarks, “Was it so that those strange trilobitic-looking

fishes of that era had to endure the buffeting of ice-waves, and to

struggle amidst the wreck of ice-floes and the crush of bergs?”[160]

_Australia._—A conglomerate similar to that of Scotland has been found

in Victoria, Australia, by Mr. Selwyn, at several localities. Along

the Wild Duck Creek, near Heathcote, and also near the Mia-Mia, Spring

Plains, Redesdale, localities in the Colony of Victoria, where it was

examined by Messrs. Taylor and Etheridge, Junior, this conglomerate

consists of a mixture of granite pebbles and boulders of various

colours and textures, porphyries, indurated sandstone, quartz, and

a peculiar flint-coloured rock in a matrix of bluish-grey very hard

mud-cement.[161] Rocks similar to the pebbles and blocks composing the

conglomerate do not occur in the immediate neighbourhood; and from the

curious mixture of large and small angular and water-worn fragments

it was conjectured that it might possibly be of glacial origin.

Scratched stones were not observed, although a careful examination was

made. From similar mud-pebble beds on the Lerderderg River, Victoria,

Mr. P. Daintree obtained a few pebbles grooved after the manner of

ice-scratched blocks.[162]

And the existence of a warm condition of climate during the Old Red

Sandstone period is evidenced by the fossiliferous limestones of

England, Russia, and America. On the banks of the Athabasca River,

Rupert-Land, Sir John Richardson found beds of limestone containing

_Producti_, _Spiriferi_, an _Orthis_ resembling _O. resupinata_,

_Terebratula reticularis_,[163] and a _Pleurotomaria_, which, in the

opinion of the late Dr. Woodward, who examined the specimens, are

characteristic of Devonian rocks of Devonshire.

CARBONIFEROUS PERIOD.

_France._—It is now a good many years since Mr. Godwin-Austen directed

attention to what he considered evidence of ice-action during the coal

period. This geologist found in the carboniferous strata of France

large angular blocks which he could not account for without inferring

the former action of ice. “Whether from local elevation,” he says,

“or from climatic conditions, there are certain appearances over the

whole which imply that at one time the temperature must have been very

low, as glacier-action can alone account for the presence of the large

angular blocks which occur in the lowest detrital beds of many of the

southern coal-basins.”[164]

_Scotland._—In Scotland great beds of conglomerate are met with in

various parts, which are now considered by Professor Geikie, Mr.

James Geikie, and other officers of the Geological Survey who have

had opportunities of examining them, to be of glacial origin. “They

are,” says Mr. James Geikie, “quite unstratified, and the stones often

show that peculiar blunted form which is so characteristic of glacial

work.”[165] Many of the stones found by Professor Geikie, several of

which I have had an opportunity of seeing, are well striated.

In 1851 Professor Haughton brought forward at the Geological Society

of Dublin, a case of angular fragments of granite occurring in the

carboniferous limestone of the county of Dublin; and he explained the

phenomena by the supposition of the transporting power of ice.

_North America._—In one of the North American coal-fields Professor

Newberry found a boulder of quartzite 17 inches by 12 inches, imbedded

in a seam of coal. Similar facts have also been recorded both in the

United States, and in Nova Scotia. Professor Dawson describes what he

calls a gigantic esker of Carboniferous age, on the outside of which

large travelled boulders were deposited, probably by drift-ice; while

in the swamps within, the coal flora flourished.[166]

_India._—Mr. W. T. Blanford, of the Geological Survey of India, states

that in beds considered to be of Carboniferous age are found large

boulders, some of them as much as 15 feet in diameter. The bed in

which these occur is a fine silt, and he refers the deposition of the

boulders to ice-action. Within the last three years his views have

received singular confirmation in another part of India, where beds

of limestone were found striated below certain overlying strata. The

probability that these appearances are due, as Mr. Blanford says, to

the action of ice, is strengthened by the consideration that about five

degrees farther to the north of the district in question rises the

cold and high table-land of Thibet, which during a glacial epoch would

undoubtedly be covered with ice that might well descend over the plains

of India.[167]

_Arctic Regions._—A glacial epoch during the Carboniferous age may be

indirectly inferred from the probable existence of warm inter-glacial

periods, as indicated by the limestones with fossil remains found in

arctic regions.

That an equable condition of climate extended to near the north pole

is proved by the fact that in the arctic regions vast masses of

carboniferous limestone, having all the characters of the mountain

limestone of England, have been found. “These limestones,” says

Mr. Isbister, “are most extensively developed in the north-east

extremity of the continent, where they occupy the greater part of

the coast-line, from the north side of the Kotzebue Sound to within

a few miles of Point Barrow, and form the chief constituent of the

lofty and conspicuous headlands of Cape Thomson, Cape Lisburn, and

Cape Sabine.”[168] Limestone of the same age occurs extensively

along the Mackenzie River. The following fossils have been found

in these limestones:—_Terebratula resupinata_,[169] _Lithostrotion

basaltiforme_, _Cyathophyllum dianthum_, _C. flexuosum_, _Turbinolia

mitrata_, _Productus Martini_,[170] _Dentalium Sarcinula_,

_Spiriferi_, _Orthidæ_, and encrinital fragments in the greatest

abundance.

Among the fossils brought home from Depôt Point, Albert Land, by

Sir E. Belcher, Mr. Salter found the following, belonging to the

Carboniferous period:—_Fusulina hyperborea_, _Stylastrea inconferta_,

_Zaphrentis ovibos_, _Clisiophyllum tumulus_, _Syringopora (Aulopora)_,

_Fenestella Arctica_, _Spirifera Keilhavii_, _Productus cora_, _P.

semireticulatus_.[171]

Coal-beds of Carboniferous age are extensively developed in arctic

regions. The fuel is of a highly bituminous character, resembling, says

Professor Haughton, the gas coals of Scotland. The occurrence of coal

in such high latitudes indicates beyond doubt that a mild and temperate

condition of climate must, during some part of the Carboniferous age,

have prevailed up to the very pole.

“In the coal of Jameson’s Land, on the east side of Greenland, lying

in latitude 71°, and in that of Melville Island, in latitude 75° N.,

Professor Jameson found plants resembling fossils of the coal-fields of

Britain.”[172]

PERMIAN PERIOD.

_England._—From the researches of Professor Ramsay in the Permian

breccias, we have every reason to believe that during a part of the

Permian age our country was probably covered with glaciers reaching

to the sea. These brecciated stones, he states, are mostly angular

or subangular, with flattened sides and but very slightly rounded at

the edges, and are imbedded in a deep red marly paste. At Abberley

Hill some of the masses are from 2 to 3 feet in diameter, and in one

of the quarries, near the base of Woodbury Hill, Professor Ramsay

saw one 2 feet in diameter. Another was observed at Woodbury Rock, 4

feet long, 3 feet broad, and 1½ feet thick. The boulders were found

in South Staffordshire, Enville, in Abberley and Malvern Hills,

and other places. “They seem,” he says, “to have been derived from

the conglomerate and green, grey, and purple Cambrian grits of the

Longmynd, and from the Silurian quartz-rocks, slates, felstones,

felspathic ashes, greenstones, and Upper Caradoc rocks of the country

between the Longmynd and Chirbury. But then,” he continues, “the south

end of the Malvern Hills is from forty to fifty miles, the Abberleys

from twenty-five to thirty-five miles, Enville from twenty to thirty

miles, and South Staffordshire from thirty-five to forty miles distant

from that country.”[173]

It is physically impossible, Professor Ramsay remarks, that these

blocks could have been transported to such distances by any other

agency than that of ice. Had they been transported by water, supposing

such a thing possible, they would have been rounded and water-worn,

whereas many of these stones are flat slabs, and most of them have

their edges but little rounded. And besides many of them are highly

polished, and others grooved and finely striated, exactly like those of

the ancient glaciers of Scotland and Wales. Some of these specimens are

to be seen in the Museum of Practical Geology, Jermyn Street.

_Scotland._—In the Island of Arran, Mr. E. A. Wunsch and Mr. James

Thomson found a bed of conglomerate which they considered of Permian

age, and probably of glacial origin. This conglomerate enclosed angular

fragments of various schistose, volcanic, and limestone rocks, and

contained carboniferous fossils.

_Ireland._—At Armagh, Ireland, Professor Hull found boulder beds of

Permian age, containing pebbles and boulders, sometimes 2 feet in

diameter. Some of the boulders must have been transported from a

region lying about 30 miles to the north-west of the locality in which

they now occur. It is difficult to conceive, says Professor Hull,

how rock fragments of such a size could have been carried to their

present position by any other agency than that of floating ice. This

boulder-bed is overlaid by a recent bed of boulder clay. Professor

Ramsay, who also examined the section, agrees with Professor Hull that

the bed is of Permian age, and unquestionably of ice-formation.[174]

Professor Ramsay feels convinced that the same conclusions which he has

drawn in regard to the Permian breccia of England will probably yet be

found to hold good in regard to much of that of North Germany.[175] And

there appears to be some ground for concluding that the cold of that

period even reached to India.[176]

_South Africa._—An ancient boulder clay, supposed to be either

of Permian or Jurassic age, has been extensively found in Natal,

South Africa. This deposit, discovered by Dr. Sutherland, the

Surveyor-General of the colony, is thus described by Dr. Mann:—

“The deposit itself consists of a greyish-blue argillaceous matrix,

containing fragments of granite, gneiss, graphite, quartzite,

greenstone, and clay-slate. These imbedded fragments are of various

size, from the minute dimensions of sand-grains up to vast blocks

measuring 6 feet across, and weighing from 5 to 10 tons. They are

smoothed, as if they had been subject to a certain amount of attrition

in a muddy sediment; but they are not rounded like boulders that

have been subjected to sea-breakers. The fracture of the rock is not

conchoidal, and there is manifest, in its substance, a rude disposition

towards wavy stratification.”

“Dr. Sutherland inclines to think that the transport of vast massive

blocks of several tons’ weight, the scoring of the subjacent surfaces

of sandstone, and the simultaneous deposition of minute sand-grains

and large boulders in the same matrix, all point to one agency as the

only one which can be rationally admitted to account satisfactorily

for the presence of this remarkable formation in the situations in

which it is found. He believes that the boulder-bearing clay of Natal

is of analogous nature to the great Scandinavian drift, to which it

is certainly intimately allied in intrinsic mineralogical character;

that it is virtually a vast moraine of olden time; and that ice, in

some form or other, has had to do with its formation, at least so far

as the deposition of the imbedded fragments in the amorphous matrix are

concerned.”[177]

In the discussion which followed the reading of Dr. Sutherland’s paper,

Professor Ramsay pointed out that in the Natal beds enormous blocks of

rock occurred, which were 60 or 80 miles from their original home, and

still remained angular; and there was a difficulty in accounting for

the phenomena on any other hypothesis than that suggested.

Mr. Stow, in his paper on the Karoo beds, has expressed a similar

opinion regarding the glacial character of the formation.[178]

But we have in the Karoo beds evidence not only of glaciation, but of a

much warmer condition of things than presently exists in that latitude.

This is shown from the fact that the shells of the _Trigona_-beds

indicate a tropical or subtropical condition of climate.

_Arctic Regions._—The evidence which we have of the existence of a

warm climate during the Permian period is equally conclusive. The

close resemblance of the _flora_ of the Permian period to that of

Carboniferous times evidently points to the former prevalence of a warm

and equable climate. And the existence of the magnesian limestone in

high latitudes seems to indicate that during at least a part of the

Permian period, just as during the accumulation of the carboniferous

limestone, a warm sea must have obtained in those latitudes.

OOLITIC PERIOD.

_North of Scotland._—There is not wanting evidence of something like

the action of ice during the Oolitic period.[179]

In the North of Scotland Mr. James Geikie says there is a coarse

boulder conglomerate associated with the Jurassic strata in the east

of Sutherland, the possibly glacial origin of which long ago suggested

itself to Professor Ramsay and other observers. Mr. Judd believes the

boulders to have been floated down by ice from the Highland mountains

at the time the Jurassic strata were being accumulated.

_North Greenland._—During the Oolitic period a warm condition of

climate extended to North Greenland. For example, in Prince Patrick’s

Island, at Wilkie Point, in lat. 76° 20′ N., and long. 117° 20′

W., Oolitic rocks containing an ammonite (_Ammonites McClintocki_,

Haughton), like _A. concavus_ and other shells of Oolitic species,

were found by Captain McClintock.[180] In Katmai Bay, near Behring’s

Straits, the following Oolitic fossils were discovered—_Ammonites

Wasnessenskii_, _A. biplex_, _Belemnites paxillosus_, and _Unio

liassinus_.[181] Captain McClintock found at Point Wilkie, in Prince

Patrick’s Island, lat. 76° 20′, a bone of _Ichthyosaurus_, and Sir E.

Belcher found in Exmouth Island, lat. 76° 16′ N., and long. 96° W., at

an elevation of 570 feet above the level of the sea, bones which were

examined by Professor Owen, and pronounced to be those of the same

animal.[182] Mr. Salter remarks that at the time that these fossils

were deposited, “a condition of climate something like that of our own

shores was prevailing in latitudes not far short of 80° N.”[183] And

Mr. Jukes says that during the Oolitic period, “in latitudes where

now sea and land are bound in ice and snow throughout the year, there

formerly flourished animals and plants similar to those living in our

own province at that time. The questions thus raised,” continues Mr.

Jukes, “as to the climate of the globe when cephalopods and reptiles

such as we should expect to find only in warm or temperate seas,

could live in such high latitudes, are not easy to answer.”[184] And

Professor Haughton remarks, that he thinks it highly improbable that

any change in the position of land and water could ever have produced a

temperature in the sea at 76° north latitude which would allow of the

existence of ammonites, especially species so like those that lived

at the same time in the tropical warm seas of the South of England

and France at the close of the Liassic, and commencement of the Lower

Oolitic period.[185]

The great abundance of the limestone and coal of the Oolitic system

shows also the warm and equable condition of the climate which must

have then prevailed.

CRETACEOUS PERIOD.

_Croydon._—A large block of crystalline rock resembling granite was

found imbedded in a pit, on the side of the old London and Brighton

road near Purley, about two miles south of Croydon. Mr. Godwin-Austen

has shown conclusively that it must have been transported there by

means of floating ice. This boulder was associated with loose sea-sand,

coarse shingle, and a smaller boulder weighing twenty or twenty-five

pounds, and all water-worn. These had all sunk together without

separating. Hence they must have been firmly held together, both during

the time that they were being floated away, and also whilst sinking to

the bottom of the cretaceous sea. Mr. Godwin-Austen supposes the whole

to have been carried away frozen to the bottom of a mass of ground-ice.

When the ice from melting became unable to float the mass attached to

it, the whole would then sink to the bottom together.[186]

_Dover._—While the workmen were employed in cutting the tunnel on

the London, Chatham, and Dover Railway, between Lydden Hill and

Shepherdswell, a few miles from Dover, they came upon a mass of coal

imbedded in chalk, at a depth of 180 feet. It was about 4 feet square,

and from 4 to 10 inches thick. The coal was friable and highly

bituminous. It resembled some of the Wealden or Jurassic coal, and

was unlike the true coal of the coal-measures. The specific gravity

of the coal precluded the supposition that it could have floated away

of itself into the cretaceous sea. “Considering its friability,” says

Mr. Godwin-Austen, “I do not think that the agency of a floating tree

could have been engaged in its transport; but, looking at its flat,

angular form, it seems to me that its history may agree with what I

have already suggested with reference to the boulder in the chalk

at Croydon. We may suppose that during the Cretaceous period some

bituminous beds of the preceding Oolitic period lay so as to be covered

with water near the sea-margin, or along some river-bank, and from

which portions could be carried off by ice, and so drifted away, until

the ice was no longer able to support its load.”[187]

Mr. Godwin-Austen then mentions a number of other cases of blocks

being found in the chalk. In regard to those cases he appropriately

remarks that, as the cases where the occurrence of such blocks has

been observed are likely to be far less numerous than those which have

escaped observation, or failed to have been recorded, and as the chalk

exposed in pits and quarries bears only a most trifling proportion to

the whole horizontal extent of the formation, we have no grounds to

conclude that the above are exceptional cases.

Boulders have also been found in the cretaceous strata of the Alps by

Escher von der Linth.[188]

The existence of warm periods during the Cretaceous age is plainly

shown by the character of the flora and fauna of that age. The fact

that chalk is of organic origin implies that the climate must have

been warm and genial, and otherwise favourable to animal life. This is

further manifested by such plants as _Cycas_ and _Zamia_, which betoken

a warm climate, and by the corals and huge sauroid reptiles which then

inhabited our waters.

It is, in fact, the tropical character of the fauna of that period

which induced Sir Charles Lyell to reject Mr. Godwin-Austen’s idea that

the boulders found in the chalk had been transported by floating ice.

Such a supposition, implying a cold climate, “is,” Sir Charles says,

“inconsistent with the luxuriant growth of large chambered univalves,

numerous corals, and many fish, and other fossils of tropical forms.”