CHAPTER X.

THE DATE OF THE GLACIAL PERIOD.

In approaching the subject of glacial chronology, we are compelled

to recognise at the outset the approximate character of all our

calculations. Still, we shall find that there are pretty well-defined

limits of time beyond which it is not reasonable to place the date of

the close of the Glacial period; and, where exact figures cannot be

determined, it may yet be of great interest and importance to know

something near the limits within which our speculations must range.

For many years past Mr. Croll's astronomical theory as to the cause of

the Glacial period has been considered in certain circles as so nearly

established that it has been adopted by them as a chronological table in

which to insert a series of supposed successive Glacial epochs which are

thought to have characterised not merely the Quaternary epoch but all

preceding geological eras. What we have already said, however, respecting

the weakness of Mr. Croll's theory is probably sufficient to discredit it

as a chronological apparatus. We will therefore turn immediately to the

more tangible evidences bearing upon the subject.

The data directly relating to the length of time which separates the

present from the Glacial period are mainly connected with two classes of

facts:

1. The amount of erosion which has been accomplished by the river systems

since the Glacial period; and 2. The amount of sedimentation which

has taken place in lakes and kettle-holes. We will consider first the

evidence from erosion.

[Illustration: Fig. 103.--Diagram of eccentricity and precession:

Abscissa represents time and ordinates, degrees of eccentricity and also

of cold. The dark and light shades show the warmer and colder winters,

and therefore indicate each 10,500 years, the whole representing a period

of 300,000 years.]

The gorge below Niagara Falls affords an important chronometer for

measuring the time which has elapsed since a certain stage in the

recession of the great North American ice-sheet. As already shown, the

present Niagara River is purely a post-glacial line of drainage;[EA] the

preglacial outlet to Lake Erie having been filled up by glacial deposits,

so that, on the recession of the ice, the lowest level between Lake Erie

and Lake Ontario was in the line of the trough of the present outlet.

But, from what has already been said, it also appears that the Niagara

River did not begin to flow until considerably after the ice-front had

withdrawn from the escarpment at Queenston, where the river now emerges

from its cañon to the low shelf which borders Lake Ontario. For a

considerable period afterwards the ice continued to block up the easterly

and northerly outlets through the valleys of the Mohawk and of the St.

Lawrence, and held the water in front of the ice up to the level of the

passes leading into the Mississippi Valley. Niagara River, of course, was

not born until these ice-barriers on the east and northeast melted away

sufficiently to allow the drainage to take its natural course.

[Footnote EA: See above, p. 200 _et seq._]

[Illustration: Fig. 104.--Map of the Niagara River below the falls,

showing the buried channel from the whirlpool to St. Davids. Small

streams, _a_, _b_, _c_, fall into the main gorge over a rocky escarpment.

No rock appears in the channel at _d_, but the rocky escarpment reappears

at _e_.]

Of these barriers, that across the Mohawk Valley doubtless gave way

first. This would allow the confluent waters of this great glacial lake

to fall down to the level of the old outlet from the basin of Lake

Ontario into the Mohawk Valley, in the vicinity of Home, N. Y. The

moment, however, that the water had fallen to this level, the plunging

torrents of Niagara would begin their work; and the gorge extending from

Queenston up to the present falls is the work done by this great river

since that point of time in the Glacial period when the ice-barrier

across the Mohawk Valley broke away.

The problem is therefore a simple one. Considering the length of

this gorge as the dividend, the object is to find the rate of annual

recession; this will be the divisor. The quotient will be the number of

years which have elapsed since the ice first melted away from the Mohawk

Valley. We are favoured in our calculation by the simplicity of the

geologic arrangement.

The strata at Niagara dip slightly to the south, but not enough to make

any serious disturbance in the problem. That at the surface, over which

the water now plunges, consists of hard limestone, seventy or eighty

feet in thickness, and this is continuous from the falls to the face of

the escarpment at Queenston, where the river emerges from the gorge.

Immediately underneath this hard superficial stratum there is a stratum

of soft rock, of about the same thickness, which disintegrates readily.

As a consequence, the plunging water continually undermines the hard

stratum at the surface, and prepares the way for it to fall down, from

time to time, in huge blocks, which are, in turn, ground to powder by

the constant commotion in which they are kept, and thus the channel is

cleared of _débris_.

[Illustration: Fig. 105.--Section of strata along the Niagara gorge from

the falls to the lake: 1, 3, strata of hard rock; 2, 4, of soft rock.]

Below these two main strata there is considerable variation in the

hardness of the rock, as shown in the accompanying diagram, where 3 and

5 are hard strata separated by a soft stratum. In view of this fact it

seems probable that, for a considerable period in the early part of the

recession, instead of there being simply one, there was a succession of

cataracts, as the water unequally wore back through the harder strata,

numbered 5, 3, and 1; but, after having receded half the distance, these

would cease to be disturbing influences, and the problem is thus really

the simple one of the recession through the strata numbered 1 and 2,

which are continuous. So uniform in consistency are these throughout the

whole distance, that the rate of recession could never have been less

than it is now. We come, therefore, to the question of the rapidity with

which the falls are now receding.

In 1841 Sir Charles Lyell and Professor James Hall (the State Geologist

of New York) visited the falls together, and estimated that the rate of

recession could not be greater than one foot a year, which would make the

time required about thirty-five thousand years. But Lyell thought this

rate was probably three times too large; so that he favoured extending

the time to one hundred thousand years. Before this the eminent French

geologist Desor had estimated that the recession could not have been

more than a foot in a century, which would throw the beginning of the

gorge back more than three million years. But these were mere guesses

of eminent men, based on no well-ascertained facts; while Mr. Bakewell,

an eminent English geologist, trusting to the data furnished him by the

guides and the old residents of Niagara, had, even then, estimated that

the rate of recession was as much as three feet a year, which would

reduce the whole time required to about ten thousand years.

But the visit of Lyell and Hall in 1841 led to the beginning of more

accurate calculations. Professor Hall soon after had a trigonometrical

survey of the falls made, from which a map was published in the State

geological report. From this and from the monuments erected, we have had

since that time a basis of comparison in which we could place absolute

confidence.

In recent years three surveys have been made: the first by the New

York State Geologists, in 1875; and the third by Mr. R. S. Woodward,

the mathematician of the United States Geological Survey, in 1886. The

accompanying map shows the outlines of the falls at the time of these

three measurements, from 1842 to 1886. According to Mr. Woodward, "the

length of the front of the Horseshoe Fall is twenty-three hundred feet.

Between 1842 and 1875 four and a quarter acres of rock were worn away by

the recession of the falls. Between 1875 and 1886 a little over one acre

and a third disappeared in a similar manner, making in all, from 1842 to

1886, about five and a half acres removed, and giving an annual rate of

recession of about two feet and a half per year for the last forty-five

years. But in the central parts of the curve, where the water is deepest,

the Horseshoe Fall retreated between two hundred and two hundred and

seventy-five feet in the eleven years between 1875 and 1886."

[Illustration: Fig. 106.--Map showing the recession of the Horseshoe

Falls since 1842, as by survey mentioned in the text (Pohlman). (by

courtesy of the American Institute of Mining Engineers.)]

It will be perceived that the recession in the centre of the Horseshoe is

very much more rapid than that nearer the margin; yet this rate at the

centre is more nearly the standard of calculation than is that near the

margin, for the gorge constantly tends to enlarge itself below the falls,

and so gradually to bring itself into line with the full-formed channel.

Taking all things into account, Mr. Woodward and the other members of

the Geological Survey thought it not improbable that the average rate

of actual recession in the Horseshoe Fall was as great as five feet per

annum; and that, if we can rely upon the uniformity of the conditions in

the past, seven thousand years is as long a period as can be assigned to

its commencement.

The only condition in the problem about which there can be much chance of

question relates to the constancy of the volume of water flowing in the

Niagara channel. Mr. Gilbert had suggested that, as a consequence of the

subsidence connected with the closing portions of the Glacial period, the

water of the Great Lakes may have been largely diverted from its present

outlet in Niagara River and turned northeastward, through Georgian Bay,

French River, and Lake Nipissing, into a tributary of the Ottawa River,

and so carried into the St. Lawrence below Lake Ontario. Of this theory

there is also much direct evidence. A well-defined shore line of rounded

pebbles extends, at an elevation of about fifty feet, across the col

from Lake Nipissing to the head-waters of the Mattawa, a tributary of

the Ottawa; while at the junction with the Ottawa there is an enormous

delta terrace of boulders, forming a bar across the main stream just such

as would result from Mr. Gilbert's supposed outlet. But this outlet was

doubtless limited to a comparatively few centuries, and Dr. Robert Bell

thinks the evidence still inconclusive.[EB]

[Footnote EB: See Bul. Geol. Soc. Am., vol. iv, pp. 423-427, vol. v, pp.

620-626.]

A second noteworthy glacial chronometer is found in the gorge of

the Mississippi River, extending from the Falls of St. Anthony, at

Minneapolis, to its junction with the preglacial trough of the old

Mississippi, at Fort Snelling, a distance likewise of about seven miles.

Above Fort Snelling the preglacial gorge is occupied by the Minnesota

River, and, as we have before stated, extends to the very sources of

this river, and is continuous with the southern portion of the valley of

the trough of the Red River of the North. Before the Glacial period the

drainage of the present basin of the upper Mississippi joined this main

preglacial valley, not at Fort Snelling, but some little distance above,

as shown upon our map.[EC] This part of the preglacial gorge became

partially filled up with glacial deposits, but it can be still traced

by the lakelets occupying portions of the old depression, and by the

records of wells which have been sunk along the line. When the ice-front

had receded beyond the site of Minneapolis, the only line of drainage

left open for the water was along the course of the present gorge from

Minneapolis to Fort Snelling.

[Footnote EC: See above, p. 209.]

Here, as at Niagara, the problem is comparatively simple. The upper

strata of rock consist of hard limestone, which is underlaid by a soft

sandstone, which, like the underlying shale at Niagara, is eroded faster

than the upper strata, and so a perpendicular fall is maintained. The

strata are so uniform in texture and thickness that, with the present

amount of water in the river, the rate of recession of the falls must

have been, from the beginning, very constant. If, therefore, the rate can

be determined, the problem can be solved with a good degree of confidence.

Fortunately, the first discoverer of the cataract--the Catholic

missionary Hennepin--was an accurate observer, and was given to

recording his observations for the instruction of the outside world and

of future generations. From his description, printed in Amsterdam in

1704, Professor N. H. Winchell is able to determine the precise locality

of the cataract when discovered in 1680.

Again, in 1766 the Catholic missionary Carver visited the falls, and not

only wrote a description, but made a sketch (found in an account of his

travels, published in London in 1788) which confirms the inferences drawn

from Hennepin's narrative. The actual period of recession, however (which

Professor Winchell duly takes into account), extends only to the year

1856, at which time such artificial changes were introduced as to modify

the rate of recession and disturb further calculations. But between 1680

and 1766 the falls had evidently receded about 412 feet. Between 1766 and

1856 the recession had been 600 feet. The average rate is estimated by

Professor Winchell to be about five feet per year, and the total length

of time required for the formation of the gorge above Fort Snelling

is a little less than eight thousand years, or about the same as that

calculated by Messrs. Woodward and Gilbert for the Niagara gorge.

To these calculations of Professor Winchell it does not seem possible

to urge any valid objection. It does not seem credible that the amount

of water in the Mississippi should ever have been less than now, while

during the continuance of the ice in the upper portion of the Mississippi

basin the flow of water was certainly far greater than now.

If any one is inclined to challenge Professor Winchell's interpretation

of the facts, even a hasty visit to the locality will suffice to produce

conviction. The comparative youth of the gorge from Fort Snelling up to

Minneapolis is evident: 1. From its relative narrowness, when compared

with the main valley below. This is represented by the shading upon

the map. The gorge from Fort Snelling up is not old enough to have

permitted much enlargement by the gradual undermining of the superficial

strata on either side, which slowly but constantly goes on. 2. From

the abruptness with which it merges into the preglacial valley of the

Minnesota-Mississippi. The opening at Fort Snelling is not Y-shaped,

as in gorges where there has been indefinite time for the operation of

erosive agencies. 3. Furthermore, the precipices lining the post-glacial

gorge above Fort Snelling are far more abrupt than those in the

preglacial valley below, and they give far less evidence of weathering.

4. Still, again, the tributary streams, like the Minnehaha River, which

empty into the Mississippi between Fort Snelling and Minneapolis,

flow upon the surface, and have eroded gorges of very limited extent;

whereas, below Fort Snelling, the small streams have usually either found

underground access to the river or occupy gorges of indefinite extent.

The above estimates, setting such narrow limits to post-glacial time

in America, will seem surprising only to those who have not carefully

considered the glacial phenomena of various kinds to be observed all

over the glaciated area. As already said, the glaciated portion of

North America is a region of waterfalls, caused by the filling up of

old channels with glacial _débris_, and the consequent diversion of the

water-courses. By this means the streams in countless places have been

forced to fall over precipices, and to begin anew their work of erosion.

Waterfalls abound in the glaciated region because post-glacial time is

so short. Give these streams time enough, and they will wear their way

back to their sources, as the preglacial streams had done over the same

area, and as similar streams have done outside the glaciated region. Upon

close observation, it will be found that the waterfalls in America are

nearly all post-glacial, and that their work of erosion has been confined

to a very limited time. A fair example is to be seen at Elyria, Ohio,

in the falls of Black River, one of the small streams which empty into

Lake Erie from the south. Its post-glacial gorge, worn in sandstone which

overlies soft shale, is only about two thousand feet in length, and it

has as yet made no approach toward a V-shaped outlet.

The same impression of recent age is made by examining the outlets of

almost any of the lakes which dot the glaciated area. The very reason of

the continued existence of these lakes is that they have not had time

enough to lower their outlets sufficiently to drain the water off, as has

been done in all the unglaciated region. In many cases it is easy to see

that the time during which this process of lowering the outlets has been

going on cannot have been many thousand years.

The same impression is made upon studying the evidences of post-glacial

valley erosion. Ordinary streams constantly enlarge their troughs by

impinging against the banks now upon one side and now upon the other, and

transporting the material towards the sea. It is estimated by Wallace

that nine-tenths of the sedimentary material borne along by rivers is

gathered from the immediate vicinity of its current, and goes to enlarge

the trough of the stream. Upon measuring the cubical contents of many

eroded troughs of streams in the glaciated region, and applying the

tables giving the average amount of annual transportation of sediment

by streams, we arrive at nearly the same results as by the study of the

recession of post-glacial waterfalls.

Professor L. E. Hicks, of Granville, Ohio, has published the results

of careful calculations made by him, concerning the valley of Raccoon

Creek in Licking County, Ohio.[ED] These show that fifteen thousand

years would be more than abundant time for the erosion of the immediate

valley adjoining that small stream. I have made and published similar

calculations concerning Plum Creek, at Oberlin, in Lorain County,

Ohio.[EE] Like Raccoon Creek, this has its entire bed in glacial

deposits, and has had nothing else to do since its birth but to enlarge

its borders. The drainage basin of the creek covers an area of about

twenty-five square miles. Its main trough averages about twenty feet in

depth by five hundred in width, along a distance of about ten miles. From

the rate at which the stream is transporting sediment, it is incredible

that it could have been at work at this process more than ten thousand

years without producing greater results.

[Footnote ED: See Baptist Quarterly for July. 1884.]

[Footnote EE: See Ice Age in North America, p. 469.]

Calculations based upon the amount of sediment deposited since the

retreat of the ice-sheet point to a like moderate conclusion. When one

looks upon the turbid water of a raging stream in time of flood, and

considers that all the sediment borne along will soon settle down upon

the bottom of the lake into which the stream empties, he can but feel

surprised that the "wash" of the hills has not already filled up the

depression of the lake. It certainly would have done so had the present

condition of things existed for an indefinite period of time.

Naturally, while prosecuting the survey of the superficial geology of

Minnesota, Mr. Upham was greatly impressed by the continued existence

of the innumerable lakelets that give such a charm to the scenery of

that State. Every day's investigations added to the evidence that the

lapse of time since the Ice age must have been comparatively brief,

since, otherwise, the rains and streams would have filled these basins

with sediment, and cut outlets low enough to drain them dry, for in many

instances he could see such changes slowly going forward.[EF]

[Footnote EF: Minnesota Geological Report for 1879, p. 73.]

[Illustration: Fig. 107.--Section of kettle-hole near Pomp's Pond,

Andover, Massachusetts (see text). (For general view of the situation,

see Fig. 30, p. 78.)]

Some years ago I myself made a careful estimate of the amount of

deposition and vegetable accumulation which had taken place in a

kettle-hole near Pomp's Pond, in Andover, Mass. The diameter of the

depression at the rim was 276 feet. The inclination of the sides was

such that the extreme depression of the apex of the inverted cone could

not have been more than seventy feet; yet the accumulation of peat and

sediment only amounted to a depth of seventeen feet. The total amount of

material which had accumulated would be represented by a cone ninety-six

feet in diameter at the base and seventeen feet at the apex, which would

equal only a deposit of about five feet over the present surface of the

bottom. It is easy to see that ten thousand years is a liberal allowance

of time for the accumulation of five feet of sediment in the bottom

of an enclosure like a kettle-hole, for upon examination it is clear

that whatever insoluble material gets into a kettle-hole must remain

there, since there is no possible way by which it can get out. Now five

feet is sixty inches, and if this amount has been six thousand years

in accumulating, that would represent a rate of an inch in one hundred

years, while, if it has been twelve thousand years in accumulation, the

rate will be only one two-hundredth of an inch per year, a film so small

as to be almost inappreciable. If we may judge from appearance, the

result would not be much different in the case of the tens of thousands

of kettle-holes and lakelets which dot the surface of the glaciated

region.

In the year 1869 Dr. E. Andrews, of Chicago, made an important series of

calculations concerning the rate at which the waters of Lake Michigan are

eating into the shores and washing the sediment into deeper water or

towards the southern end of the lake. With reference to the erosion of

the shores, it appears from the work of the United States Coast Survey

that a shoulder, covered with sixty feet of water, representing the

depth at which wave-action is efficient in erosion, extends outward from

the west shore a distance of about three miles, where the sounding line

reveals the shore of the deeper original lake as it appeared upon the

first withdrawal of the ice.

From a variety of observations the average rate at which the erosion of

the bluffs is proceeding is found to be such that the post-glacial time

cannot be more than ten thousand years, and probably not more than seven

thousand.

An independent mode of calculating this period is afforded by the

accumulations of sand at the south end of the lake, to which it is

constantly drifting by the currents of water propelled against the shores

by the wind; for the body of water in the lake is moving southward

along the shores towards the closed end in that direction, there being

a returning current along the middle of the lake. All the railroads

approaching Chicago from the east pass through these sand deposits, and

few of the observant travellers passing over the routes can have failed

to notice the dunes into which the sand has been drifted by the wind.

Now, all the material of these dunes and sand-beaches has been washed out

of the bluffs to the northward by the process already mentioned, and has

been slowly transferred by wave-action to its present position. It is

estimated that south of Chicago and Grand Haven, this wave-transported

sand amounts to 3,407,451,000 cubic yards. This occupies a belt curving

around the south end about ten miles wide and one hundred miles long.

The rate at which the sand is moving southward along the shore is found

by observing the amount annually arrested by the piers at Chicago, Grand

Haven, and Michigan City. This equals 129,000 cubic yards for a year,

which can scarcely be more than one quarter or one fifth of the total

amount in motion. At this rate, the sand accumulations at the southern

end of the lake would have been produced in a little less than seven

thousand years.

"If," says Dr. Andrews, "we estimate the total annual sand-drift at

only twice the amount actually stopped by the very imperfect piers

built--which, in the opinion of the engineers, is setting it far too

low--and compare it with the capacity of the clay-basin of Lake Michigan,

we shall find that, had this process continued one hundred thousand years

the whole south end of Lake Michigan, up to the line connecting Chicago

and Michigan City, would have been full and converted into dry land

twenty-five thousand years ago, and the coast-line would now be found

many miles north of Chicago."[EG]

[Footnote EG: Southall's Recent Origin of Man, p. 502.]

It is proper to add a word in answer co an objection which may arise

in the reader's mind, for it will doubtless occur to some to ask why

this sand which is washed out by the waves from the bluffs is not

carried inward towards the deeper portion of the trough of the lake,

thus producing a waste which would partly counteract the forces of

accumulation at the south end. The answer is found in the fact that the

south end of Lake Michigan is closed, and that the currents set in motion

by the wind are such that there is no off-shore motion sufficient to move

sand, and, as a matter of fact, dredgings show that the sand is limited

to the vicinity of the shore.

By comparing the eroded cliffs upon Michigan and the other Great Lakes

with what occurs in similar situations about the glacial Lake Agassiz, we

obtain an interesting means of estimating the comparative length of time

occupied by the ice-front in receding from the Canadian border to Hudson

Bay.

As we have seen, Lake Agassiz occupied a position quite similar in most

respects to Lake Michigan. Its longest diameter was north and south, and

the same forces which have eroded the cliffs of Lake Michigan and piled

up sand-dunes at its southern end would have produced similar effects

upon the shores of Lake Agassiz, had its continuance been anywhere near

as long as that of the present Lake Michigan has been. But, according

to Mr. Upham, who has most carefully surveyed the whole region, there

are nowhere on the shores of the old Lake Agassiz any evidence of eroded

cliffs at all to be compared with those found upon the present Great

Lakes, while there is almost an entire lack of sand deposits about the

south end such as characterise the shore of Lake Michigan. "The great

tracts of dunes about the south end of Lake Michigan belong," as Upham

well observes, "wholly to beach accumulations, being sand derived from

erosion of the western and eastern shores of the lake.... But none of

the beaches of our glacial lakes are large enough to make dunes like

those on Lake Michigan, though the size and depth of Lake Agassiz, its

great extent from north to south, and the character of its shores, seem

equally favorable for their accumulation. It is thus again indicated that

the time occupied by the recession of the ice-sheet was comparatively

brief."[EH]

[Footnote EH: Proceedings of the Boston Society of Natural History,

vol. xxiv, p. 454; Upham's Glacial Lakes in Canada, in Bulletin of the

Geological Society of America, vol. ii, p. 248.]

From Mr. Upham's conclusions it would seem that if ten thousand years

be allowed for the post-glacial existence of Lake Michigan, one tenth

of that period would be more than sufficient to account for the cliffs,

deltas, beaches, and other analogous phenomena about Lake Agassiz. In

other words, the duration of Lake Agassiz could not have been more

than a thousand years, which gives us a measure of the rate at which

the recession of the ice-front went on after it had withdrawn to the

international boundary. The distance from there to the mouth of Nelson

River is about 600 miles. The recession of the ice-front over that area

proceeded, therefore, at the average rate of about half a mile per year.

There are many evidences that the main period of glaciation west of the

Rocky Mountains was considerably later than that in the eastern part of

the continent. A portion of the facts pointing to this conclusion have

been well stated by Mr. George F. Becker, of the United States Geological

Survey.

"No one," he says, "who has examined the glaciated regions of the

Sierra can doubt that the great mass of the ice disappeared at a very

recent period. The immense areas of polished surfaces fully exposed

to the severe climate of say from 7,000 to 12,000 feet altitude, the

insensible erosion of streams running over glaciated rocks, and the

freshness of erratic boulders are sufficient evidence of this. There

is also evidence that the glaciation began at no very distant geologic

date. As Professor Whitney pointed out, glaciation is the last important

geological phenomenon and succeeded the great lava flows. There is also

much evidence that erosion has been trifling since the commencement of

glaciation, excepting under peculiar circumstances. East of the range,

for example, at Virginia City, andesites which there is every reason to

suppose preglacial have scarcely suffered at all from erosion, so that

depressions down which water runs at every shower are not yet marked with

water-courses, while older rocks, even of Tertiary age and close by,

are deeply carved. The rainfall at Virginia City is, to be sure, only

about ten inches, so that rock would erode only say one third as fast

as on the California coast; but even when full allowance is made for

this difference, it is clear that these andesites must be much younger

than the commencement of glaciation in the northeastern portion of the

continent as usually estimated. So, too, the andesites near Clear Lake,

in California, though beyond a doubt preglacial, have suffered little

erosion, and one of the masses, Mount Konocti (or Uncle Sam), has nearly

as characteristic a volcanic form as Mount Vesuvius."[EI]

[Footnote EI: Bulletin of the Geological Society of America, vol. ii, pp.

196, 197.]

This view of Mr. Becker is amply sustained by many other obvious facts,

some of which may be easily observed by tourists who visit the Yosemite

Park. The freedom of the abutting walls of this cañon from talus, as well

as the freshness of the glacial scratches upon both the walls and the

floor of the tributary cañons, all indicate a lapse of centuries only,

rather than of thousands of years, since their occupation by glacial ice.

The freshness of the high-level terraces surrounding the valleys of Great

Salt Lake, in Utah, and of Pyramid and North Carson Lakes, in Nevada, and

the small amount of erosion which has taken place since the formation of

these terraces, point in the same direction--namely, to a very recent

date for the glaciation of the Pacific coast.

We have already detailed the facts concerning the formation of these

terraces and the evidence of their probable connection with the Glacial

period. It is sufficient, therefore, here to add that, according to Mr.

Russell and Mr. Gilbert (two of the most eminent members of the United

States Geological Survey, who have each published monographs minutely

embodying the results of their extensive observations in this region),

the erosion of present streams in the beds which were deposited during

the enlargement of the lakes is very slight, and the modification of the

shores since the formation of the high terraces has been insignificant.

According to Mr. Gilbert: "The Bonneville shores are almost unmodified.

Intersecting streams, it is true, have scored them and interrupted their

continuity for brief spaces; but the beating of the rain has hardly

left a trace. The sea-cliffs still stand as they first stood, except

that frost has wrought upon their faces so as to crumble away a portion

and make a low talus at the base. The embankments and beaches and bars

are almost as perfect as though the lake had left them yesterday, and

many of them rival in the symmetry and perfection of their contours the

most elaborate work of the engineer. There are places where boulders of

quartzite or other enduring rock still retain the smooth, glistening

surfaces which the waves scoured upon them by clashing against them the

sands of the beach.

"When this preservation is compared with that of the lowest Tertiary

rocks of the region--the Pliocene beds to which King has given the name

Humboldt--the difference is most impressive. The Pliocene shore-lines

have disappeared.

"The deposits are so indurated as to serve for building-stone. They have

been upturned in many places by the uplifting of mountains. Elsewhere

they have been divided by faults, and the fragments, dissevered from

their continuation in the valley, have been carried high up on the

mountain-flanks, where erosion has carved them in typical mountain

forms.... The date of the Bonneville flood is the geologic yesterday,

and, calling it yesterday, we may without exaggeration refer the Pliocene

of Utah to the last decade; the Eocene of the Colorado basin to the last

century, and relegate the laying of the Potsdam sandstone to prehistoric

times."[EJ]

[Footnote EJ: Second Annual Report of the United States Geological

Survey, p. 188.]

Mr. Russell adds to this class of evidence that of the small extent to

which the glacial striæ have been effaced since the withdrawal of the

ice from the borders of these old lakes: "The smooth surfaces are still

scored with fine, hair-like lines, and the eye fails to detect more

than a trace of disintegration that has taken place since the surfaces

received their polish and striation.... It seems reasonable to conclude

that in a severe climate like that of the high Sierra it" (the polish)

"could not remain unimpaired for more than a few centuries at the

most."[EK]

[Footnote EK: See also Mr. Upham in American Journal of Science, vol.

xli, pp. 41, 51.]

Europe does not seem to furnish so favourable opportunities as America

for estimating the date of the Glacial period; still it is not altogether

wanting in data bearing upon the subject.

Some of the caves in which palæolithic implements were found associated

with the bones of extinct animals in southern England contain floors

of stalagmite which have been thought by some to furnish a measure of

the time separating the deposits underneath from those above. This is

specially true in the case of Kent's Cavern, near Torquay, which contains

two floors of stalagmite, the upper one almost continuous and varying in

thickness from sixteen inches to five feet, the lower one being in places

twelve feet thick, underneath which human implements were found.

But it is difficult to determine the rate at which stalagmite

accumulates. As is well known, this deposit is a form of carbonate of

lime, and accumulates when water holding the substance in solution drops

down upon the surface, where it is partially evaporated. It then leaves a

thin film of the substance upon the floor. The rate of the accumulation

will depend upon both the degree to which the water is saturated with the

carbonate and upon the quantity of the water which percolates through the

roof of the cavern. These factors are so variable, and so dependent upon

unknown conditions in the past, that it is very difficult to estimate the

result for any long period of time. Occasionally a quarter of an inch of

stalagmite accretion has been known to take place in a cavern in a single

year, while in Kent's Cavern, over a visitor's name inscribed in the

year 1688, a film of stalagmite only a twentieth of an inch in thickness

has accumulated. If, therefore, we could reckon upon a uniformity of

conditions stretching indefinitely back into the past, we could determine

the age of these oldest remains of man in Kent's Hole by a simple sum in

arithmetic, and should infer that the upper layer of stalagmite required

240,000 years, and the lower 576,000 years, for their growth, which would

carry us back more than 700,000 years, and some have not hesitated to

affix as early a date as this to these lowest implement-bearing gravels.

But other portions of the cave show an actual rate of accretion very much

larger. Six inches of stalagmite is there found overlying some remains of

Romano-Saxon times which cannot be more than 2,000 years old. Assuming

this as the uniform rate, the total time required for the deposit of the

stalagmitic floors would still be about 70,000 years. But, as we have

seen, the present rates of deposition are probably considerably less than

those which took place during the moister climate of the Glacial epoch.

Still, even by supposing the rate to be increased fourfold, the age of

this lower stratum would be reduced to only 12,000 years. So that, as Mr.

James Geikie well maintains, "Even on the most extravagant assumption as

to the former rate of stalagmitic accretion, we shall yet be compelled

to admit a period of many thousands of years for the formation of the

stalagmitic pavements in Kent's Cavern."[EL] We should add, however,

that there is much well-founded doubt whether the implements found

in the lowest stratum were really in place, since, according to Dr.

Evans, "Owing to previous excavations and to the presence of burrowing

animals, the remains from above and below the stalagmite have become

intermingled."[EM]

[Footnote EL: Prehistoric Europe, p. 83.]

[Footnote EM: Stone and Flint Implements, p. 446.]

An attempt was made by M. Morlot in Switzerland to obtain the chronology

of the Glacial period by studying the deltas of the streams descending

the glaciated valleys. He paid special attention to that of the Tinière,

a stream which flows into Lake Geneva near Villeneuve. The modern delta

of this stream consists of gravel and sand deposited in the shape of a

flattened cone, and investigations upon it were facilitated by a long

railroad cutting through it. "Three layers of vegetable soil, each of

which must at one time have formed the surface of the cone, have been

cut through at different depths."[EN] In the upper stratum Roman tiles

and a coin were found; in the second stratum, unvarnished pottery and

implements of bronze; while in the lower stratum, at a depth of nineteen

feet from the surface, a human skull was found, to which Morlot assigned

an age of from 5,000 to 7,000 years.

[Footnote EN: Lyell's Antiquity of Man, p. 28.]

But Dr. Andrews, after carefully revising the data, felt confident that

the time required for the whole deposit of this lower delta was not more

than 5,000 years, and that the oldest human remains in it, which were

about half way from between the base and the surface of the cone, were

probably not more than 3,000 years old.

Still, the significance of this estimate principally arises from the

relation of the modern delta to older deltas connected with the Glacial

period. Above this modern delta, formed by the river in its present

proportions, there is another, more ancient, about ten times as large,

whose accumulation doubtless took place upon the final retreat of the

ice from Lake Geneva. No remains of man have been found in this, but it

doubtless corresponds in age with the high-level gravels in the valley

of the Somme, in which the remains of man and the mammoth, together with

other extinct animals, have been found.

We do not see, however, that any very definite calculation can be made

concerning the time required for its deposition. Lyell was inclined to

consider it ten times as old as the modern delta, simply upon the ground

of its being ten times as large. On Morlot's estimate of the age of the

modern delta, therefore, the retreat of the ice whose melting torrents

deposited the upper delta would be fixed at 100,000 years ago, and upon

Dr. Andrews's calculation, at about 20,000.

But it is evident that the problem is not one of simple multiplication.

The floods of water which accompanied the melting back of the ice from

the upper portions of this valley must have been immensely larger than

those of the present streams, and their transporting power immensely

greater still. Hence we do not see that any conclusions can be drawn from

the deltas of the Tinière to give countenance to extreme views concerning

the date of the close of the Glacial period.[EO]

[Footnote EO: Lyell's Antiquity of Man, p. 321.]

In the valley of the Somme the chronological data relating to the Glacial

period, and indicating a great antiquity for man, have been thought to

be more distinct than anywhere else in Europe. As already stated, it

is the prevalent opinion that since man first entered the valley, in

connection with the mammoth and the other extinct animals characteristic

of the Glacial period, the trough of the Somme, about a mile in width and

a hundred feet in depth, has been eroded by the drainage of its present

valley. An extensive accumulation of peat also has taken place along the

bottom of the trough of the river since it was originally eroded to its

present level. This substance occurs all along the bottom of the valley

from far above Amiens to the sea, and is in some places more than thirty

feet in depth. The animal and vegetable remains in it all belong to

species now inhabiting Europe.

The depth of the peat indicates that when it was formed the land stood

at a slightly higher elevation than now, for the base of the stratum is

now below the sea-level, while the peat is of fresh-water origin, and,

according to Dr. Andrews,[EP] is formed from the vegetable accumulations

connected with forest growths. When, therefore, the country was covered

with forests, as it was in prehistoric times, the accumulation must have

proceeded with considerable rapidity. This inference is confirmed by the

occurrence in the peat of prostrate trunks of oak, four feet in diameter,

so sound that they were manufactured into furniture. The stumps of trees,

especially of the birch and alder, were also found in considerable

number, standing erect where they grew, sometimes to a height of three

feet. Now, as Dr. Andrews well remarks, it is evident that, in order

to prevent these stumps and prostrate trunks from complete decay, the

accumulation of peat must have been rapid. From certain Roman remains

found six feet and more beneath the surface, he estimates that the

accumulation since the Roman occupation has been as much as six inches a

century, at which rate the whole would take place in somewhat over 5,000

years.

[Footnote EP: American Journal of Science, October, 1868.]

Still, if we accept this estimate, we have obtained but a starting-point

from which to estimate the age of the high-level gravels in which

palæolithic implements were found; for, if we accept the ordinary theory,

we must add to this the time required for the river to lower its bed from

eighty to a hundred feet, and to carry out to the sea the contents of

its wide trough. But, as already shown, the Glacial period was, even in

the north of France, a time of great precipitation and of a considerable

degree of cold, when ice formed to a much greater extent than now upon

the surface of the Somme. The direct evidence of this consists in the

boulders mingled with the high-level gravel which are of such size as to

require floating ice for their transportation.

In addition to the natural increase in the eroding power of the Somme

brought about by the increase in its volume, on account of the greater

precipitation in the Glacial age, there would also be, as Prestwich has

well shown, a great increase in rate through the action of ground-ice,

which plays a very important part in the river erosion of arctic

countries, and in all probability did so during the Glacial period in the

valley of the Somme.

"When the water is reduced to and below 32° Fahr., although the rapid

motion may prevent freezing on the surface for a time, any pointed

surfaces at the bottom of the river, such as stones and boulders, will

determine (as is the case with a saturated saline solution) a sort of

crystallisation, needles of ice being formed, which gradually extend from

stone to stone and envelop the bodies with which they are in contact. By

this means the whole surface of a gravelly river-bed may become coated

with ice, which, on a change of temperature, or of atmospheric pressure,

or on acquiring certain dimensions and buoyancy, rises to the surface,

bringing with it the loose materials to which it adhered. Colonel Jackson

remarks, in speaking of this bottom-ice, that 'it frequently happens that

these pieces, in rising from the bottom, bring up with them sand and

stones, which are thus transported by the current.... When the thaw sets

in the ice, becoming rotten, lets fall the gravel and stones in places

far distant from those whence they came.'

"Again, Baron Wrangell remarks that, 'in all the more rapid and rocky

streams of this district [northern Siberia] the formation of ice takes

place in two different manners; a thin crust spreads itself along the

banks and over the smaller bays where the current is least rapid; but the

greater part is formed in the bed of the river, in the hollows among the

stones, where the weeds give it the appearance of a greenish mud. As soon

as a piece of ice of this kind attains a certain size, it is detached

from the ground and raised to the surface by the greater specific gravity

of the water; these masses, containing a quantity of gravel and weeds,

unite and consolidate, and in a few hours the river becomes passable

in sledges instead of in boats.' Similar observations have been made

in America; but instances need not be multiplied, as it is a common

phenomenon in all arctic countries, and is not uncommon on a small scale

even in our latitudes.

"The two causes combined--torrential river-floods and rafts of

ground-ice, together with the rapid wear of the river cliffs by

frost--constituted elements of destruction and erosion of which our

present rivers can give a very inadequate conception; and the excavations

of the valleys must have proceeded with a rapidity with which the present

rate of erosion cannot be compared; and estimates of time founded on

this, like those before mentioned on surface denudation, are therefore

not to be relied upon."[EQ]

[Footnote EQ: Prestwich's Geology, vol. ii, pp. 471, 472.]

Speaking a little later of taking the present rates of river erosion as a

standard to estimate the chronology of the Glacial period, the same high

authority remarks: "It no more affords a true and sufficient guide than

it would be to take the tottering paces and weakened force of an old man

as the measure of what that individual was, and what he could do, in his

robust and active youth. It may be right to take the effects at present

produced by a given power as the known quantity, a, but it is equally

indispensable, in all calculations relative to the degree of those

forces in past times, to take notice of the unknown quantity, x, although

this, in the absence of actual experience, which cannot be had, can only

be estimated by the results and by a knowledge of the contemporaneous

physical conditions. It may be a complicated equation, but it is not to

be avoided.[ER]

[Footnote ER: Prestwich's Geology, vol. ii, pp. 520, 521.]

"In this country and in the north of France broad valleys have been

excavated to the depth of from about eighty to a hundred and fifty feet

in glacial and post-glacial times. Difficult as it is by our present

experience to conceive this to have been effected in a comparatively

short geological term, it is equally, and to my mind more, difficult to

suppose that man could have existed eighty thousand years or more, and

that existing forms of our fauna and flora should have survived during

two hundred and forty thousand years without modification or change."[ES]

[Footnote ES: Ibid., p. 533.]

The discussion of the age of the high-level river gravels of the Somme

and other streams in northwestern Europe is not complete, however,

without considering another possibility as to the mode of their

deposition. The conclusion to which Mr. Alfred Tylor arrived, after a

prolonged and careful study of the subject, was that the main valleys of

the Somme and other streams in northern France and southern England were

preglacial in their origin, and that the accumulations of gravel at high

levels along their margin were due to enormous floods which characterised

the closing portion of the great ice age, which he denominated the

pluvial period.[ET] The credibility of floods large enough to accomplish

the results manifest in the valley of the Somme is supported by reference

to a flood which occurred on the Mulleer River, in India, in 1856, when

a stream, which is usually insignificant, was so swollen by a rainfall

of a single day that it rose high enough to sweep away an iron bridge the

bottoms of whose girders were sixty-five feet above high-water mark. One

iron girder weighing eighty tons was carried two miles down the river,

and nearly buried in sand. The significance of these facts is enhanced

by observing also that for fifteen miles above the bridge the fall of

the river only averaged ten feet per mile. Floods to this extent are

not uncommon in India. During the Glacial period spring freshets, must

have been greatly increased by the melting of a large amount of snow and

ice which had accumulated during the winter, and also by the formation

of ice-gorges near the mouths of many of the streams. It is probable,

also, that the accumulation of ice across the northern part of the German

Ocean may have permanently flooded the streams entering that body of

water; for it is by no means improbable that there was a land connection

between England and France across the Straits of Dover until after the

climax of the Glacial period. In support of his theory, Mr. Tylor points

to the fact "that the gravel in the valley of the Somme at Amiens is

partly derived from _débris_ brought down by the river Somme and by the

two rivers the Celle and the Arve, and partly consists of material from

the adjoining higher grounds washed in by land floods," and that the

"Quaternary gravels of the Somme are not separated into two divisions by

an escarpment of chalk parallel to the river," but "thin out gradually as

they slope from the high land down to the Somme."

Mr. Tylor's reasoning seems especially cogent to one who stands on the

ground where he can observe the size of the valley and the diminutive

proportions of the present stream. Even if we do not grant all that is

claimed by Mr. Tylor, it is difficult to resist the main force of his

argument, and to avoid the conclusion that the valley of the Somme is

largely the work of preglacial erosion, and has been, at any rate, only

in slight degree deepened and enlarged during post-Tertiary time.

[Footnote ET: Proceedings of the Geological Society, London, November 8,

1867, pp. 103-126: Quarterly Journal of the Geological Society, February

1, 1869, pp. 57-100.]

Summary.

In briefly summarising our conclusions concerning the question of man's

antiquity as affected by his known relations to the Glacial period, it is

important, first, to remark upon the changes of opinion which have taken

place with respect to geological time within the past generation. Under

the sway of Sir Charles Lyell's uniformitarian ideas, geologists felt

themselves at liberty to regard geological time as practically unlimited,

and did not hesitate to refer the origin of life upon the globe back to

a period of 500,000,000 years. In the first edition of his Origin of

Species Charles Darwin estimated that the time required for the erosion

of the Wealden deposits in England was 306,662,400 years, which he spoke

of as "a mere trifle" of that at command for establishing his theory of

the origin of species through natural selection. In his second edition,

however, he confesses that his original statement concerning the length

of geological time was rash; while in later editions he quietly omitted

it.

Meanwhile astronomers and physicists have been gradually setting limits

to geological time until they have now reached conclusions strikingly

in contrast with those held by the mass of English geologists forty

years ago. Mr. George H. Darwin, Professor of Mathematics at Cambridge

University, has from a series of intricate calculations shown that

between fifty and one hundred million years ago the earth was revolving

from six to eight times faster than now, and that the moon then almost

touched the earth, and revolved about it once every three or four hours.

From this proximity of the moon to the earth, it would result that if the

oceans had been then in existence the tides would have been two hundred

times as great as now, creating a wave six hundred feet in height,

which would sweep around the world every four hours. Such a condition

of things would evidently be incompatible with geological life, and

geology must limit itself to a period which is inside of 100,000,000

years. Sir William Thomson and Professor Tait, of Great Britain, and

Professor Newcomb, of the United States Naval Observatory, approaching

the question from another point of view, seem to demonstrate that the

radiation of heat from the sun is diminishing at a rate such that ten

or twelve million years ago it must have been so hot upon the earth's

surface as to vaporise all the water, and thus render impossible the

beginning of geological life until later than that period. Indeed, they

seem to prove by rigorous mathematical calculations that the total amount

of heat originally possessed by the nebula out of which the sun has been

condensed would only be sufficient to keep up the present amount of

radiation for 18,000,000 years.

The late Dr. Croll, feeling the force of these astronomical conclusions,

thought it possible to add sufficiently to the sun's heat to extend its

rule backwards approximately 100,000,000 years by the supposition of a

collision with it of another moving body of near its own size. Professor

Young and others have thought that possibly the heat of the sun might

have been kept up by the aid of the impact of asteroids and meteorites

for a period of 30,000,000 years. Mr. Wallace obtains similar figures by

estimating the time required for the deposition of the stratified rocks

open to examination upon the land surface of the globe. As a result of

his estimates, it would appear that 28,000,000 years is all the time

required for the formation of the geological strata. From all this it is

evident that geologists are much more restricted in their speculations

involving time than they thought themselves to be a half-century ago.

Taking as our standard the medium results attained by Wallace, we shall

find it profitable to see how this time can be portioned out to the

geological periods, that we may ascertain how much approximately can be

left for the Glacial epoch.

On all hands it is agreed that the geological periods decrease in length

as they approach the present time. According to Dana's estimates,[EU]

the "ratio for the Palæozoic, Mesozoic, and Cenozoic periods would be

12:3:1"--that is, Cenozoic time is but one sixteenth of the whole.

This embraces the whole of the Tertiary period, during which placental

mammals have been in existence, together with the post-Tertiary or

Glacial period, extending down to the present time; that is, the time

since the beginning of the Tertiary period and the existence of the

higher animals is considerably less than two million years, even upon Mr.

Wallace's basis of calculation. But if we should be compelled to accept

the calculations of Sir William Thomson, Professor Tait, and Professor

Newcomb, the Cenozoic period would be reduced to considerably less than

one million years. It is difficult to tell how much of Cenozoic time is

to be assigned to the Glacial period, since there is, in fact, no sharply

drawn line between the two periods. The climax of the Glacial period

represented a condition of things slowly attained by the changes of level

which took place during the latter part of the Tertiary epoch.

[Footnote EU: See revised edition of his Geology, p. 586.]

In order to estimate the degree of credibility with which we may at

the outset regard the theory of Mr. Prestwich and others, that all the

phenomena of the Glacial period can be brought within the limits of

thirty or forty thousand years, it is important to fix our minds upon

the significance of the large numbers with which we are accustomed to

multiply and divide geological quantities.[EV]

[Footnote EV: See Croll's Climate and Time, chap. xx.]

Few people realise either the rapidity with which geological changes

are now proceeding or the small amount of change which might produce a

Glacial period, and fewer still have an adequate conception of how long a

period a million years is, and how much present geological agencies would

accomplish in that time. At the present rate at which erosive agencies

are now acting upon the Alps, their dimensions would be reduced one half

in a million years. At the present rate of the recession of the Falls of

St. Anthony, the whole gorge from St. Louis to Minneapolis would have

been produced in a million years. A river lowering its bed a foot in a

thousand years would produce a cañon a thousand feet deep in a million

years.

If we suppose the Glacial period to have been brought about by an

elevation of land in northern America and northern Europe, proceeding at

the rate of three feet a century, which is that now taking place in some

portions of Scandinavia, this would amount to three thousand feet in one

hundred thousand years, and that is probably all, and even more than all,

which is needed. One hundred thousand years, therefore, or even less,

might easily include both the slow coming on of the Glacial period and

its rapid close. Prestwich estimates that the ice now floating away from

Greenland as icebergs is sufficient if accumulating on a land-surface

to extend the borders of a continental glacier about four hundred and

fifty feet a year, or one mile in twelve years, one hundred miles in

twelve hundred years, and seven hundred miles (about the limit of glacial

transportation in America) in less than ten thousand years.

After making all reasonable allowances, therefore, Prestwich's conclusion

that twenty-five thousand years is ample time to allow to the reign

of the ice of the Glacial period cannot be regarded as by any means

incredible or, on _a priori_ grounds, improbable.

APPENDIX.

THE TERTIARY MAN.

By Professor Henry W. Haynes.

"It must not be imagined that it is in any way proved that the

Palæolithic man was the first human being that existed. We must be

prepared to wait, however, for further and better authenticated

discoveries before carrying his existence back in time further than

the Pleistocene or post-Tertiary period."[EW] This was the position

assumed more than twelve years ago by the eminent English geologist

and archæologist, Dr. John Evans, and it was still maintained in his

address before the Anthropological Section of the British Association on

September 18, 1890. I believe that the study of all the evidence in favor

of the existence of the Tertiary man that has been brought forward down

to the present time will leave the question in precisely the same state

of uncertainty.

[Footnote EW: _A Few Words on Tertiary Man_, Trans, of Hertfordshire Nat.

Hist. Soc, vol. i, p. 150.]

"In order to establish the existence of man at such a remote period the

proofs must be convincing. It must be shown, first, that the objects

found are of human workmanship; secondly, that they are really found as

stated; and, thirdly, the age of the beds in which they are found must be

clearly ascertained and determined."[EX] These tests I propose to apply

to the evidence for the Tertiary man recently brought forward in Europe,

and then to consider the significance of certain discoveries on the

Pacific coast of our own continent.

[Footnote EX: Ibid., p. 148.]

Tertiary deposits in Europe are alleged to have supplied three sorts of

evidence of this fact: _First_, the bones of man himself; _second_, bones

of animals showing incisions or fractures supposed to have been produced

by human agency; _third_, chipped flints believed to exhibit marks of

design in their production.

A very complete survey of the question of the antiquity of man was

published in 1883 by M. Gabriel de Mortillet, one of its most eminent

investigators, under the title of Le Préhistorique. In that work he

subjected to a most rigid examination all the evidence for Tertiary man,

coming under either of these three heads, that had been brought forward

up to that date.

The instances of the discovery of human bones in Europe were two--at

Colle del Vento, in Savona, and Castenedolo, near Brescia, both in Italy.

At the former site, in a Pliocene marine deposit abounding in fossil

oysters and containing some _scattered_ bones of fossil mammals, a human

skeleton was found _with the bones lying in their natural connection_.

Mortillet, however, and many others regard this as an instance of a

subsequent interment rather than as proof that the man lived in Pliocene

times.[EY] At Castenedolo, in a similar marine Pliocene formation, on

three different occasions human skeletons have been discovered, but

in different strata. One investigator has accounted for these as the

result of a shipwreck in the Pliocene period. This bold hypothesis not

only requires that man should have been sufficiently advanced at that

very remote period to have navigated the sea, but it calls for two

shipwrecks, at different times, at the same point. It has, however, since

been abandoned by its author in favor of the presumption of subsequent

interments, as in the previous instance.[EZ]

[Footnote EY: This is also the opinion of Hamy, _Précis de Paléontologie

Humaine_, p. 67. Professor Le Conte, _Elements of Geology_ (third

edition, 1891), p. 609, is wrong in attributing the opposite conclusion

to Hamy, on the evidence of "flint implements found in this locality."]

[Footnote EZ: Bullettino di Paletnologia Italiana, tome xv, p. 109

(August 18, 1889).]

Animal bones showing cuts or breaks supposed to be the work of man have

been found in seventeen different localities in Europe. They can all,

however, be accounted for as the result of natural movements or pressure

of the soil acting in connection with sharp substances, like fractured

flints, or else as having been made by the teeth of sharks, whose fossil

remains are found in great abundance in the same formation.

All the discoveries of flints supposed to show traces of intentional

chipping are pronounced to be unsatisfactory, with the exception of

those found in three localities--Thenay (near Tours) and Puy-Courny

(near Aurillac), in France, and Otta, in the valley of the Tagus, in

Portugal. As European archæologists at the present time are substantially

in accord with Mortillet in restricting the discussion to these three

places, I will follow their example. But although Mortillet believes

that flints found at all these localities exhibit marks of intelligent

action, he will not admit that they are the work of man. He attributes

them to an intelligent ancestor of man, whom he calls by the name

of anthropopithecus, or the precursor of man. Of this creature he

distinguishes three different species, named respectively after the

discoverers of the flints in the three localities just mentioned. The

precursor, however, has found up to this time only a very limited

acceptance among men of science, although a few believe in him on purely

theoretical grounds. The discussion generally turns upon the question

whether these flints were chipped intentionally or are the result of

natural causes; and also upon the determination of the geological age of

the formations in which they are found.

[Illustration: Fig. 108.--Flint flakes collected by Abbé Bourgeois from

Miocene strata at Thenay (after Gaudry). Natural size.]

I visited Thenay, the most celebrated of these three localities, in 1877,

and had the advantage of studying the question there under the guidance

of the late Abbé Bourgeois, the discoverer of the flints, and one of the

most prominent advocates of the Tertiary man. This was the year before

he died, and he showed me at the time his complete collection, and gave

me several of the objects he had discovered. Geologists are agreed in

assigning the deposits in which they occur to the lower Miocene or middle

Tertiary period, which restricts the discussion to the character of the

flints themselves. The accompanying woodcut[FA] gives some indication

of their appearance, although it is misleading, because the long figure

resembling a flint knife is intended to represent a solid nucleus. None

of these objects, however, ought to be called "flints flakes," as very

few, if any, flakes showing the "bulb of percussion," always seen upon

them, have been discovered in the Tertiary deposits at Thenay,[FB]

although I have found them there myself _upon the surface_. The three

other figures would be classed by archæologists as "piercers," as

Bourgeois has himself designated them, and are also solid objects. Many

of the Thenay flints exhibit a "crackled" appearance, due to the action

of heat. On this account Mortillet maintains that they were splintered

by fire, and not formed by percussion, the usual method by which flint

implements were fabricated in the stone age. The Thenay objects are

all of very small dimensions, and are so absolutely unlike the large,

rudely-chipped axes of the Chellean type, found in so many different

parts of the world, and generally accepted as the implement used by

Palæolithic man, that the question naturally suggests itself, What could

have been the purpose for which these little implements were employed? No

better answer has been suggested than the ludicrous one that they were

used by the hairy anthropopithecus to rid himself of the vermin with

which he was infested.

[Footnote FA: From Le Conte, _op. cit._, p. 608. The figures are copied

from Gaudry, who borrowed them from the article by Bourgeois, _Congrès

Internat. de Bruxelles_, 1872, p. 89, pl. ii; and from his _La Question

de l'Homme Tertiare_. Revue des Questions Scientifiques, 1877, p. 15.]

[Footnote FB: Le Préhistorique, p. 91.]

But, leaving aside the question of their purpose, let us consider

the evidence presented by the flints themselves. Do they exhibit the

unmistakable traces of intentional chipping produced by a series of

slight blows or thrusts, delivered in regular succession and in the

same direction, with the result of forming a distinctly marked edge?

And does the appearance of the action of fire upon their surface imply

the intervention of intelligence? To both questions M. Adrien Arcelin,

the well-known geologist of Mâcon, has given very sufficient replies in

the negative. He has discovered numerous objects of precisely similar

appearance in Eocene deposits in the neighborhood of Mâcon.[FC] But,

instead of pushing man back on this account so much further into the

past, he accounts for the marks of chipping to be seen on many of these

objects as the result of the accidental shocks of one stone against

another in the countless overturnings and movements to which the

strata have been subjected during the long ages of geological time. He

gives photographs of some of these objects, which are to me entirely

convincing, and describes how he has surprised Nature in the very act of

fabricating them in an abandoned quarry worked in an Eocene deposit. He

thinks the "crackled" surfaces can be readily explained as the result

of atmospheric action, or of hot springs charged with silex. Numerous

examples of similar changes in the surface of flint, that have been

noticed by himself and others in different localities, are instanced.

Even if some have been caused by fire, this does not necessarily imply

the intervention of man to have produced it. Similar discoveries have

also been made by M. d'Ault de Mesnil, at Thenay, in Eocene deposits,[FD]

and by M. Paul Cabanne, in the Gironde.[FE] My own opinion, based

upon the experience of many years spent in the study of flints broken

naturally as well as artificially, and upon a careful examination of

Bourgeois's collections, is that the so-called Thenay flints are the

result of natural causes.

[Footnote FC: Matériaux pour l'Histoire Prim, et Nat. de l'Homme, tome

xix, p. 193.]

[Footnote FD: Matériaux, ibid., p. 246.]

[Footnote FE: Id., tome xxii, p. 205.]

The second locality where flints alleged to display marks of human action

have been found is the vicinity of Aurillac, in the Auvergne, especially

on the flanks of a hill called Puy-Courny. They occur in a conglomerate

of the upper Miocene period, and are consequently much later than the

Thenay flints. In this conglomerate, in 1869, M. Tardy discovered a

worked flint flake which has every appearance of being artificial.[FF]

Mortillet, however, says that it was found in the upper surface of the

deposit, where there may easily have been a mingling with the Quaternary

formation; and it certainly resembles worked flakes, which are not

uncommon in the Quaternary. The geological determination of the find may

consequently be regarded as uncertain.

[Footnote FF: See Matériaux, tome vi, p. 94. S. Reinach, however,

_Description Raison. du Musée de Saint-Germain-en-Laye_, i, p. 107, n. 8,

calls it "gravure inexacte."]

The flints discovered at Puy-Courny by M. Barnes are of small dimensions,

and have all been produced by percussion. Many of them are said to

bear some resemblance to pointed flakes of artificial origin, and

one has been figured, probably selected for its excellence.[FG] It is

by no means convincing to me, and I am not at all surprised that so

many archæologists question the artificial character of these objects,

which exhibit a great variety of forms. Upon this point Rames does

not profess to be qualified to pronounce judgment, limiting himself

solely to the geological questions. He argues, however, that the fact

that all the objects supposed to be artificial are made of the best

qualities of flint, of which implements are ordinarily made, although

fragments of inferior quality are abundant in the same formation,

implies the intervention of man's judgment in making the selection.

But M. Boule shows that this is merely the result of the erosion of an

ancient river, which operated only upon the upper beds, in which alone

the better qualities of flint are to be found; and Rames has accepted

this explanation.[FH] The flints of Puy-Courny seem to fall within the

same category as those of Thenay. They are the product of denudation,

have travelled long distances, and have been subjected to the action of

powerful agents. These causes are sufficient to account for the shocks of

which they show the traces, and to explain the production of splinters

arising therefrom.

[Footnote FG: Matériaux, tome xviii, p. 400.]

[Footnote FH: Revue d'Anthropologie (third series), tome iv, p. 217.]

The last locality in which flints claimed to have been manufactured by

the Tertiary man are supposed to have been discovered is the so-called

desert of Otta, in the valley of the Tagus, not far from Lisbon.

The formation there is a lacustrine deposit of great thickness, belonging

to the upper Miocene, and abounding in flint. Here, during the course of

twenty years, M. Ribeiro discovered, but mostly upon the surface, a large

number of flakes of flint and quartzite. After much debate in regard to

them, ninety-five of them were finally sent by him to Paris, in 1878, and

placed in the archæological department of the great exposition. There

they were to be submitted to the judgment of the assembled prehistoric

archæologists of all nationalities, many of whom, including the writer,

availed themselves of the opportunity of carefully studying them. The

judgment of Mortillet is that twenty-two specimens exhibited unmistakable

traces of intentional chipping, in which opinion I entirely concur.

Only nine, however, were represented as coming from the Miocene, some

of which showed on their surface an incrustation of grit, which was

claimed as proof of their origin. But the opinion was freely expressed

that, even if they really came from the Miocene deposits, they might

have penetrated into them from the surface, through cracks, and thus

have become so incrusted. It was accordingly resolved to hold the next

international congress of prehistoric archæologists at Lisbon, in 1880,

mainly for the purpose of settling this question, if possible, by an

investigation conducted upon the spot. In the course of a visit made at

that time to Otta, several artificial specimens were found on the surface

by different searchers, but Professor Bellucci, of Perugia, was fortunate

enough to discover a flint flake _in situ_, still so closely imbedded

in the deposit that it required to be detached by a hammer. There is no

question that this object was actually found in a Miocene deposit, but

unfortunately it belongs to the doubtful category of external flakes,

which, although they exhibit the "bulb of percussion," have no other

sure indication that they are the work of man.[FI] As such bulbs can

be produced by natural causes, some stronger proof than this of the

existence of Tertiary man is demanded.

[Footnote FI: It has been figured by Bellucci, _Archivio per

l'Anthropologia e la Etnologia di Firenze_, tome xi, p. 12, tav. iv, fig.

2. To me it possesses no value as evidence.]

These are all the localities in Europe claimed by Mortillet to have

furnished such evidence, but he thinks a strong confirmation of it

is afforded by certain discoveries made in the auriferous gravels of

California. I will not occupy space here in repeating arguments I have

brought forward elsewhere to show the utter insufficiency of this

evidence to prove the existence of man on the Pacific coast of our

continent during the Pliocene period,[FJ] They may all be summed up in

the words of Le Conte: "The doubts in regard to this extreme antiquity

of man are of three kinds, viz.: 1. Doubts as to the Pliocene age of the

gravels--they may be early Quaternary. 2. Doubts as to the authenticity

of the finds--no scientist having seen any of them in situ. 3. Doubts

as to the undisturbed conditions of the gravels, for auriferous gravels

are especially liable to disturbance. The character of the implements

said to have been found gives peculiar emphasis to this last doubt, _for

they are not Paleolithic_, but Neolithic."[FK] The question has been

raised whether this archæological objection is applicable to the stone

mortars, numerous examples of which have been found in the gravels, some

of them quite recently.[FL] If the evidence brought forward by Professor

Whitney and others were limited to these mortars, it might very well

be claimed that they are neither Palæolithic nor Neolithic; that the

smoothness of their surface is owing to their having been hollowed out of

pebbles that have been polished and worn by natural forces. But Professor

Whitney has cited numberless instances of "spear-heads," "arrow-heads,"

"discoidal stones," "stone beads," and "a hatchet" that have been found

under precisely similar conditions as the mortars. So Mr. Becker has

recently produced an affidavit of a certain Mr. Neale that in a tunnel

run into the gravel in 1877 "between two hundred and three hundred feet

beyond the edge of the solid lava, he saw several spear-heads nearly

one foot in length."[FM] Now it cannot be questioned that such objects

as these clearly belong to the Neolithic period, which does not imply

that all the objects used at that time were polished, but that together

with chipped implements "polished stone implements were also used."[FN]

No archæologist will believe that, while Palæolithic man has not yet

been discovered in the Tertiary deposits of western Europe, the works of

Neolithic man have been found in similar deposits in western America.

Peculiar difficulties seem to surround the evidence brought forward

in support of such an assumption. We are told by Professor Whitney

that a stone mortar was "found standing upright, and the pestle was

in it, in its proper place, just as it had been left by the owner."

He fails, however, to explain how this was brought about in a gravel

deposit supposed to have been laid down by great floods of water. So,

when Mr. Neale swears that he saw fifteen years ago in the same gravels

spear-heads a great deal larger than those known to archæologists, may

we not ask whether reliance can be placed on the memory of witnesses who

testify to impossibilities to justify conclusions that rest upon such

testimony? I think we shall have to wait for further and better evidence

than this before we are called upon to admit that the existence of the

Tertiary man upon our Pacific coast has been established.

[Footnote FJ: _The Prehistoric Archæology of North America_, Narrative

and Critical History of America, vol. i, pp. 850-356.]

[Footnote FK: Le Conte, _op. cit._, p. 614.]

[Footnote FL: Professor George Frederick Wright, _Prehistoric Man on the

Pacific Coast_, Atlantic Monthly, April, 1891, p. 512; _Table Mountain

Archæology_, Nation, May 21, 1891, p. 419.]

[Footnote FM: _Antiquities from under Tuolome Table Mountain in

California_, Bulletin of the Geological Society of America, vol. ii, p.

192.]

[Footnote FN: Le Conte, _op. cit._, p. 607.]

INDEX.

Aar Glacier, 11, 43, 132.

Abbeville, France, 251, 263.

Abbott, C. C, cited, 242, 245.

Adams, Charles Francis, cited, 297.

Adhémar, cited, 307, 310.

Africa, ancient glaciers of, 191.

Agassiz, Louis, cited, 9, 11, 43, 128, 241.

Ailsa Crag, 167, 168.

Akron. Ohio, 220, 221.

Alaska, 1, 22, 23 _et seq._, 47, 212, 283;

climate of, 291, 302.

Aletsch Glacier, 9, 211, 241.

Alleghany Valley, 206, 214;

terraces in, 229.

Alpine glaciers, existing, 9-11, 43 _et seq._;

size and number of, 9;

depth of, 11;

velocity of, 43 _et seq._;

ancient, 58-60, 131-136;

advance and retreat of, 116.

Alps, 1, 9-11, 43 _et seq._, 58 _et seq._, 91, 131 _et seq._, 211;

age of, 328.

Altaville, Cal, 296.

Amazon Valley, temperature of, 316.

Amherst, Ohio, glacial marks near, 52.

Amiens, France, implements from, 252, 263 _et seq._;

terraces at, 360.

Andes, 17, 330;

age of, 328.

Andover, Mass., 77 _et seq._, 345.

Andrews, cited, 345, 347, 354, 356.

Animals, extinct, associated with man in eastern America, 262;

in France, 263;

in England, 264 _et seq._;

in Wales, 272;

in Belgium, 277 _et seq._;

summary concerning, 281-293.

Animals, relics of, in loess, 188.

Antarctic Continent, existing glaciers of, 1, 18 _et seq._

Arcy, Belgium, grotto at, 279.

Arenig Mawr, Wales, 150, 151, 172.

Argillite implement, face and side view of, 247, 259.

Arnhem, Holland, moraine at, 181.

Asia, existing glaciers in, 14 _et seq._;

ancient glaciers of, 190.

Assiniboine River, 228.

Astronomical theories of the Glacial period, 303 _et seq._

Atlantic Ocean, 314.

Aurillac, supposed flint-chips near, 367, 370.

Australia, ancient glaciers of, 126, 192.

Austria, existing glaciers of, 9.

Auvergne, 136.

Babbitt, Miss F. E., cited, 253, 254, 255.

Bakewell on age of Niagara gorge, 337.

Baldwin, C. C, 251.

Baldwin, P., 25.

Ball, cited, 310, 317.

Baltic Sea, 129.

Barnsley, England, 155.

Bates, cited, 204.

Bear, 270, 287, 290.

Bear, grizzly, 270, 288.

Beaver, 289.

Beaver Creek, Pa., 205, 230, 232.

Becker, cited, 296, 300, 349.

Bedford, England, 265.

Beech Flats, Ohio, terrace at, 217.

Belgium, human relics in glacial terraces in, 264;

caverns of, 274.

Bell, cited, 109, 117;

on unity of the Glacial period, 110.

Bellevue, Pa., glacial terrace on the Ohio at, 217.

Bellucci, cited, 372.

Ben Nevis, 240.

Bernese Oberland, 9, 59, 131, 132.

Big Stone Lake, 208, 226.

Birmingham. England, 150.

Bishop, cited. 306.

Bison, 262, 270, 271, 278, 289.

Black Forest, the, 136.

Black River, Ohio, 343.

Black Sea, 238.

Blanc, Mont, 1, 9-11, 132, 211.

Blandford, cited, 312.

Boone County, Ky., glacial deposits in, 212.

Boston, scratched stone from till of, 54;

drumlins in the vicinity of, 75.

Boston Society of Natural History, 296.

Boulder-clay. (See Till.)

Boulders, disintegrated, 57, 71.

Boulders, distribution of, in New-England, 57, 60, 61, 69 _et seq._;

in Switzerland, 58 _et seq._, 133.

Boulders, transportation of, in Pennsylvania, 57, 61, 85;

in New Hampshire, 60, 71;

in Kentucky, 63, 97;

in Ohio, 64, 72;

in Rhode Island, 67;

in Massachusetts, 69 _et seq._;

in Connecticut, 71, 72;

in New Jersey, 83;

in Illinois, 97.

Bourgeois, Abbé, cited, 367.

Bridgenorth, England, 150.

Bridlington, England, 156, 158.

Bristol Channel, 138, 178.

British Columbia, 1, 23, 121 _et seq._, 194, 198.

British Isles, ancient glaciers of, 136-181;

preglacial level of land in, 139-141;

preglacial climate in 141, 142;

great glacial centres--

Wales, 143;

Ireland, 143;

Galloway, 144;

Lake District, 144;

Pennine Chain, 144;

confluent glaciers--

Irish Sea Glacier, 145-153;

Solway Glacier, 153-158;

East Anglian Glacier, 158;

Isle of Man, 164-167;

the so-called Great Submergence, 167-180;

dispersion of erratics of Shap granite, 180, 181;

drainage of, 238;

caverns of, 267;

climate of, 314.

Brixham Cave, 267 _et seq._

Bromsgrove, England, 150.

Brooklyn, N. Y., 66, 67.

Brown, on glaciers of Greenland, 40, 41.

Brown's Valley, 226.

Bruce, skull of, 276.

Buried forests in America, 107 _et seq._

Buried outlets and channels, 199-210;

of Lake Erie, 201, 333;

of Lake Huron, 202;

of Lake Ontario, 202;

of Lake Superior, 203;

of Lake Michigan, 203;

in southwestern Ohio, 203;

near Cincinnati, 203;

near Louisville, Ky., 205;

in the Tuscarawas Valley, 205;

in the valley of the Beaver, 205;

of oil Creek, 205;

in the valley of the Alleghany, 206;

of Chautauqua Lake, 207;

near Minneapolis, 208.

Burton, England, 164.

Busk, cited, 267.

Buttermere, England, 153, 168.

Cache Valley, Utah, 233.

Cae Gwyn Cave, 148, 271 _et seq._, 280.

Caithness, Scotland, 180.

Calaveras skull, 295, 300.

California, 21, 124, 281, 287, 294, 358, 372.

Cambridgeshire, England, 158.

Canada, 94, 95.

Canstadt, man of, 279.

Canton, Ohio, 232.

Cape St. Roque, 31 3.

Caribbean Sea, 318.

Caribou, 262.

Carll, cited, 205, 207.

Carpathian Mountains, 136, 328.

Carpenter, F. R., cited, 321, 322.

Cascade Range, 21.

Caspian Sea, 238.

Cattaraugus Creek, N. Y., 220.

Caucasus Mountains, 15;

age of, 328.

Cave-bear, 269-271, 278, 280;

hyena, 269, 270, 278;

lion, 269-271, 278.

Caverns, British, 267-274;

on the Continent, 274-281.

Cefn Cave, 148, 271.

Cenis, Mont, 135.

Centres of glacial dispersion, 304 _et seq._, 323 _et seq._, 328;

in America, 113, 121;

in Europe, 129 _et seq._;

in the British Isles, 142 _et seq._

Cevennes, 136.

Chamberlin, T. C, terminal moraine of second Glacial epoch, 93,

98 _et seq._;

on driftless area, 102, 103;

cited, 110, 218, 229, 307;

on Cincinnati ice-dam, 218.

Chamois, 289, 290.

Chamouni, 132.

Charpentier, 9, 59.

Chasseron, 58, 132.

Chautauqua Lake, buried outlet of, 207.

Chenango River, 220.

Cheshire, England, 149,153,178,180.

Cheyenne River, 228.

Chicago, Ill., 346.

Chimpanzee, skull of, 276.

Chur, 133.

Cincinnati, buried channels near, 203 _et seq._;

glacial dam at, 212 _et seq._;

terraces at, 231.

Clarksburg, W. Va., 216.

Claymont, Del., 258 _et seq._;

view of implement found near, 259.

Claypole, cited, 200, 219, 221.

Climate of Glacial period, 291.

Clwyd, vale of, 147 _et seq._. 271 _et seq._

Clyde, the, 144.

Collett, cited, 107.

Colorado, 123, 124.

Columbia deposit, 245, 254 _et seq._

Columbiana County, Ohio, 232.

Comstock, cited, 307.

Conewango Creek, 232;

ancient depth of, 206.

Connecticut, 71, 72, 74, 91.

Conyers, cited, 265.

Cook on subsidence in New Jersey, 196.

Cope, cited, 288.

Cordilleran Glacier, 121 _et seq._

Corswall, England, 312.

Cows, 268.

Cresson, cited, 251, 258 _et seq._

Crevasses. (See Fissures.)

Croll, cited, 304, 307 _et seq._, 332, 362.

Cro-Magnon, rock shelter of, 281.

Cromer, England, 160.

Crosby, on composition of till, 81 _et seq._

Cross Fell escarpment, 153, 180.

Culoz, 132.

Cumberland, England, 146, 153, 168, 173.

Gumming, quoted, 166.

Gushing, H., 26

Cuyahoga River, 220, 221;

buried channel of, 200.