"We find the marks of marine animals in the most solid parts of the

earth, consequently those solid parts have been formed after the ocean

was inhabited by those animals which are proper to that fluid medium.

If, therefore, we knew the natural history of these solid parts, and

could trace the operations of the globe by which they have been formed,

we would have some means for computing the time through which those

species of animals have continued to live. But how shall we describe a

process which nobody has seen performed and of which no written history

gives any account? This is only to be investigated, first, in examining

the nature of those solid bodies the history of which we want to know;

and, secondly, in examining the natural operations of the globe, in

order to see if there now exist such operations as, from the nature of

the solid bodies, appear to have been necessary for their formation.

"There are few beds of marble or limestone in which may not be found

some of those objects which indicate the marine object of the mass. If,

for example, in a mass of marble taken from a quarry upon the top of the

Alps or Andes there shall be found one cockle-shell or piece of coral,

it must be concluded that this bed of stone has been originally formed

at the bottom of the sea, as much as another bed which is evidently

composed almost altogether of cockle-shells and coral. If one bed of

limestone is thus found to have been of marine origin, every concomitant

bed of the same kind must be also concluded to have been formed in the

same manner.

"In those calcareous strata, which are evidently of marine origin,

there are many parts which are of sparry structure--that is to say, the

original texture of those beds in such places has been dissolved, and a

new structure has been assumed which is peculiar to a certain state of

the calcareous earth. This change is produced by crystallization, in

consequence of a previous state of fluidity, which has so disposed

the concerting parts as to allow them to assume a regular shape and

structure proper to that substance. A body whose external form has

been modified by this process is called a CRYSTAL; one whose internal

arrangement of parts is determined by it is said to be of a SPARRY

STRUCTURE, and this is known from its fracture.

"There are, in all the regions of the earth, huge masses of calcareous

matter in that crystalline form or sparry state in which, perhaps, no

vestige can be found of any organized body, nor any indication that such

calcareous matter has belonged to animals; but as in other masses this

sparry structure or crystalline state is evidently assumed by the marine

calcareous substances in operations which are natural to the globe,

and which are necessary to the consolidation of the strata, it does not

appear that the sparry masses in which no figured body is formed

have been originally different from other masses, which, being only

crystallized in part, and in part still retaining their original form,

have ample evidence of their marine origin.

"We are led, in this manner, to conclude that all the strata of the

earth, not only those consisting of such calcareous masses, but others

superincumbent upon these, have had their origin at the bottom of the

sea.

"The general amount of our reasoning is this, that nine-tenths, perhaps,

or ninety-nine-hundredths, of this earth, so far as we see, have been

formed by natural operations of the globe in collecting loose materials

and depositing them at the bottom of the sea; consolidating those

collections in various degrees, and either elevating those consolidated

masses above the level on which they were formed or lowering the level

of that sea.

"Let us now consider how far the other proposition of strata being

elevated by the power of heat above the level of the sea may be

confirmed from the examination of natural appearances. The strata formed

at the bottom of the ocean are necessarily horizontal in their position,

or nearly so, and continuous in their horizontal direction or extent.

They may be changed and gradually assume the nature of each other, so

far as concerns the materials of which they are formed, but there cannot

be any sudden change, fracture, or displacement naturally in the body

of a stratum. But if the strata are cemented by the heat of fusion,

and erected with an expansive power acting below, we may expect to find

every species of fracture, dislocation, and contortion in those bodies

and every degree of departure from a horizontal towards a vertical

position.

"The strata of the globe are actually found in every possible position:

for from horizontal they are frequently found vertical; from continuous

they are broken and separated in every possible direction; and from a

plane they are bent and doubled. It is impossible that they could have

originally been formed, by the known laws of nature, in their present

state and position; and the power that has been necessarily required

for their change has not been inferior to that which might have been

required for their elevation from the place in which they have been

formed."(2)

From all this, therefore, Hutton reached the conclusion that the

elevation of the bodies of land above the water on the earth's surface

had been effected by the same force which had acted in consolidating the

strata and giving them stability. This force he conceived to be exerted

by the expansion of heated matter.

"We have," he said, "been now supposing that the beginning of our

present earth had been laid in the bottom of the ocean, at the

completion of the former land, but this was only for the sake of

distinctness. The just view is this, that when the former land of the

globe had been complete, so as to begin to waste and be impaired by

the encroachment of the sea, the present land began to appear above the

surface of the ocean. In this manner we suppose a due proportion to be

always preserved of land and water upon the surface of the globe, for

the purpose of a habitable world such as this which we possess. We

thus also allow time and opportunity for the translation of animals and

plants to occupy the earth.

"But if the earth on which we live began to appear in the ocean at

the time when the LAST began to be resolved, it could not be from the

materials of the continent immediately preceding this which we examine

that the present earth has been constructed; for the bottom of the ocean

must have been filled with materials before land could be made to appear

above its surface.

"Let us suppose that the continent which is to succeed our land is at

present beginning to appear above the water in the middle of the Pacific

Ocean; it must be evident that the materials of this great body, which

is formed and ready to be brought forth, must have been collected from

the destruction of an earth which does not now appear. Consequently,

in this true statement of the case there is necessarily required the

destruction of an animal and vegetable earth prior to the former land;

and the materials of that earth which is first in our account must have

been collected at the bottom of the ocean, and begun to be concocted for

the production of the present earth, when the land immediately preceding

the present had arrived at its full extent.

"We have now got to the end of our reasoning; we have no data further

to conclude immediately from that which actually is; but we have got

enough; we have the satisfaction to find that in nature there are

wisdom, system, and consistency. For having in the natural history of

the earth seen a succession of worlds, we may from this conclude that

there is a system in nature; in like manner as, from seeing revolutions

of the planets, it is concluded that there is a system by which they are

intended to continue those revolutions. But if the succession of worlds

is established in the system of nature, it is in vain to look for

anything higher in the origin of the earth. The result, therefore,

of our present inquiry is that we find no vestige of a beginning--no

prospect of an end."

Altogether remarkable as this paper seems in the light of later

knowledge, neither friend nor foe deigned to notice it at the moment.

It was not published in book form until the last decade of the century,

when Hutton had lived with and worked over his theory for almost fifty

years. Then it caught the eye of the world. A school of followers

expounded the Huttonian doctrines; a rival school under Werner in

Germany opposed some details of the hypothesis, and the educated world

as a whole viewed the disputants askance. The very novelty of the new

views forbade their immediate acceptance. Bitter attacks were made upon

the "heresies," and that was meant to be a soberly tempered judgment

which in 1800 pronounced Hutton's theories "not only hostile to sacred

history, but equally hostile to the principles of probability, to the

results of the ablest observations on the mineral kingdom, and to the

dictates of rational philosophy." And all this because Hutton's theory

presupposed the earth to have been in existence more than six thousand

years.

Thus it appears that though the thoughts of men had widened, in those

closing days of the eighteenth century, to include the stars, they had

not as yet expanded to receive the most patent records that are written

everywhere on the surface of the earth. Before Hutton's views could be

accepted, his pivotal conception that time is long must be established

by convincing proofs. The evidence was being gathered by William Smith,

Cuvier, and other devotees of the budding science of paleontology in

the last days of the century, but their labors were not brought to

completion till a subsequent epoch.

NEPTUNISTS VERSUS PLUTONISTS

In the mean time, James Hutton's theory that continents wear away and

are replaced by volcanic upheaval gained comparatively few adherents.

Even the lucid Illustrations of the Huttonian Theory, which Playfair,

the pupil and friend of the great Scotchman, published in 1802, did not

at once prove convincing. The world had become enamoured of the rival

theory of Hutton's famous contemporary, Werner of Saxony--the theory

which taught that "in the beginning" all the solids of the earth's

present crust were dissolved in the heated waters of a universal sea.

Werner affirmed that all rocks, of whatever character, had been formed

by precipitation from this sea as the waters cooled; that even veins

have originated in this way; and that mountains are gigantic crystals,

not upheaved masses. In a word, he practically ignored volcanic action,

and denied in toto the theory of metamorphosis of rocks through the

agency of heat.

The followers of Werner came to be known as Neptunists; the Huttonians

as Plutonists. The history of geology during the first quarter of the

nineteenth century is mainly a recital of the intemperate controversy

between these opposing schools; though it should not be forgotten that,

meantime, the members of the Geological Society of London were making

an effort to hunt for facts and avoid compromising theories. Fact and

theory, however, were too closely linked to be thus divorced.

The brunt of the controversy settled about the unstratified

rocks--granites and their allies--which the Plutonists claimed as of

igneous origin. This contention had the theoretical support of the

nebular hypothesis, then gaining ground, which supposed the earth to be

a cooling globe. The Plutonists laid great stress, too, on the observed

fact that the temperature of the earth increases at a pretty constant

ratio as descent towards its centre is made in mines. But in particular

they appealed to the phenomena of volcanoes.

The evidence from this source was gathered and elaborated by Mr. G.

Poulett Scrope, secretary of the Geological Society of England, who, in

1823, published a classical work on volcanoes in which he claimed that

volcanic mountains, including some of the highest-known peaks, are

merely accumulated masses of lava belched forth from a crevice in the

earth's crust.

"Supposing the globe to have had any irregular shape when detached from

the sun," said Scrope, "the vaporization of its surface, and, of course,

of its projecting angles, together with its rotatory motion on its axis

and the liquefaction of its outer envelope, would necessarily occasion

its actual figure of an oblate spheroid. As the process of expansion

proceeded in depth, the original granitic beds were first partially

disaggregated, next disintegrated, and more or less liquefied,

the crystals being merged in the elastic vehicle produced by the

vaporization of the water contained between the laminae.

"Where this fluid was produced in abundance by great dilatation--that

is, in the outer and highly disintegrated strata, the superior specific

gravity of the crystals forced it to ooze upward, and thus a great

quantity of aqueous vapor was produced on the surface of the globe. As

this elastic fluid rose into outer space, its continually increasing

expansion must have proportionately lowered its temperature; and, in

consequence, a part was recondensed into water and sank back towards the

more solid surface of the globe.

"And in this manner, for a certain time, a violent reciprocation of

atmospheric phenomena must have continued--torrents of vapor rising

outwardly, while equally tremendous torrents of condensed vapor, or

rain, fell towards the earth. The accumulation of the latter on the

yet unstable and unconsolidated surface of the globe constituted the

primeval ocean. The surface of this ocean was exposed to continued

vaporization owing to intense heat; but this process, abstracting

caloric from the stratum of the water below, by partially cooling it,

tended to preserve the remainder in a liquid form. The ocean will have

contained, both in solution and suspension, many of the matters carried

upward from the granitic bed in which the vapors from whose condensation

it proceeded were produced, and which they had traversed in their rise.

The dissolved matters will have been silex, carbonates, and sulphates

of lime, and those other mineral substances which water at an intense

temperature and under such circumstances was enabled to hold in

solution. The suspended substances will have been all the lighter and

finer particles of the upper beds where the disintegration had been

extreme; and particularly their mica, which, owing to the tenuity of its

plate-shaped crystals, would be most readily carried up by the ascending

fluid, and will have remained longest in suspension.

"But as the torrents of vapor, holding these various matters in

solution and suspension, were forced upward, the greater part of the

disintegrated crystals by degrees subsided; those of felspar and quartz

first, the mica being, as observed above, from the form of its plates,

of peculiar buoyancy, and therefore held longest in suspension.

"The crystals of felspar and quartz as they subsided, together with a

small proportion of mica, would naturally arrange themselves so as to

have their longest dimensions more or less parallel to the surface on

which they rest; and this parallelism would be subsequently increased,

as we shall see hereafter, by the pressure of these beds sustained

between the weight of the supported column of matter and the expansive

force beneath them. These beds I conceive, when consolidated, to

constitute the gneiss formation.

"The farther the process of expansion proceeded in depth, the more was

the column of liquid matter lengthened, which, gravitating towards

the centre of the globe, tended to check any further expansion. It is,

therefore, obvious that after the globe settled into its actual orbit,

and thenceforward lost little of its enveloping matter, the whole

of which began from that moment to gravitate towards its centre, the

progress of expansion inwardly would continually increase in rapidity;

and a moment must have at length arrived hen the forces of expansion and

repression had reached an equilibrium and the process was stopped from

progressing farther inwardly by the great pressure of the gravitating

column of liquid.

"This column may be considered as consisting of different strata, though

the passage from one extremity of complete solidity to the other of

complete expansion, in reality, must have been perfectly gradual. The

lowest stratum, immediately above the extreme limit of expansion, will

have been granite barely DISAGGREGATED, and rendered imperfectly liquid

by the partial vaporization of its contained water.

"The second stratum was granite DISINTEGRATED; aqueous vapor, having

been produced in such abundance as to be enabled to rise upward,

partially disintegrating the crystals of felspar and mica, and

superficially dissolving those of quartz. This mass would reconsolidate

into granite, though of a smaller grain than the preceding rock.

"The third stratum was so disintegrated that a greater part of the mica

had been carried up by the escaping vapor IN SUSPENSION, and that of

quartz in solution; the felspar crystals, with the remaining quartz and

mica, SUBSIDING by their specific gravity and arranging themselves in

horizontal planes.

"The consolidation of this stratum produced the gneiss formation.

"The fourth zone will have been composed of the ocean of turbid and

heated water, holding mica, etc., in suspension, and quartz, carbonate

of lime, etc., in solution, and continually traversed by reciprocating

bodies of heated water rising from below, and of cold fluid sinking from

the surface, by reason of their specific gravities.

"The disturbance thus occasioned will have long retarded the deposition

of the suspended particles. But this must by degrees have taken place,

the quartz grains and the larger and coarser plates of mica subsiding

first and the finest last.

"But the fragments of quartz and mica were not deposited alone; a great

proportion of the quartz held in SOLUTION must have been precipitated

at the same time as the water cooled, and therefore by degrees lost

its faculty of so much in solution. Thus was gradually produced the

formation of mica-schist, the mica imperfectly recrystallizing or being

merely aggregated together in horizontal plates, between which the

quartz either spread itself generally in minute grains or unified into

crystalline nuclei. On other spots, instead of silex, carbonate of lime

was precipitated, together with more or less of the nucaceous sediment,

and gave rise to saccharoidal limestones. At a later period, when the

ocean was yet further cooled down, rock-salt and sulphate of lime were

locally precipitated in a similar mode.

"The fifth stratum was aeriform, and consisted in great part of

aqueous vapors; the remainder being a compound of other elastic fluids

(permanent gases) which had been formed probably from the volatilization

of some of the substances contained in the primitive granite and carried

upward with the aqueous vapor from below. These gases will have

been either mixed together or otherwise disposed, according to their

different specific gravities or chemical affinities, and this stratum

constituted the atmosphere or aerial envelope of the globe.

"When, in this manner, the general and positive expansion of the globe,

occasioned by the sudden reduction of outward pressure, had ceased (in

consequence of the REPRESSIVE FORCE, consisting of the weight of its

fluid envelope, having reached an equilibrium with the EXPANSIVE FORCE,

consisting of the caloric of the heated nucleus), the rapid superficial

evaporation of the ocean continued; and, by gradually reducing its

temperature, occasioned the precipitation of a proportionate quantity

of the minerals it held in solution, particularly its silex. These

substances falling to the bottom, accompanied by a large proportion of

the matters held in solution, particularly the mica, in consequence of

the greater comparative tranquillity of the ocean, agglomerated these

into more or less compact beds of rock (the mica-schist formation),

producing the first crust or solid envelope of the globe. Upon this,

other stratified rocks, composed sometimes of a mixture, sometimes of

an alternation of precipitations, sediments, and occasionally of

conglomerates, were by degrees deposited, giving rise to the TRANSITION

formations.

"Beneath this crust a new process now commenced. The outer zones of

crystalline matter having been suddenly refrigerated by the rapid

vaporization and partial escape of the water they contained, abstracted

caloric from the intensely heated nucleus of the globe. These

crystalline zones were of unequal density, the expansion they had

suffered diminishing from above downward.

"Their expansive force was, however, equal at all points, their

temperature everywhere bearing an inverse ratio to their density. But

when by the accession of caloric from the inner and unliquefied nucleus

the temperature, and consequently the expansive force of the lower

strata of dilated crystalline matter, was augmented, it acted upon the

upper and more liquefied strata. These being prevented from yielding

OUTWARDLY by the tenacity and weight of the solid involucrum of

precipitated and sedimental deposits which overspread them, sustained

a pressure out of proportion to their expansive force, and were in

consequence proportionately condensed, and by the continuance of the

process, where the overlying strata were sufficiently resistant, finally

consolidated.

"This process of consolidation must have progressed from above downward,

with the increase of the expansive force in the lower strata, commencing

from the upper surface, which, its temperature being lowest, offered the

least resistance to the force of compression.

"By this process the upper zone of crystalline matter, which had

intumesced so far as to allow of the escape of its aqueous vapor and of

much of its mica and quartz, was resolidified, the component crystals

arranging themselves in planes perpendicular to the direction of the

pressure by which the mass was consolidated--that is, to the radius of

the globe. The gneiss formation, as already observed, was the result.

"The inferior zone of barely disintegrated granite, from which only

a part of the steam and quartz and none of the mica had escaped,

reconsolidated in a confused or granitoidal manner; but exhibits marks

of the process it had undergone in its broken crystals of felspar and

mica, its rounded and superficially dissolved grains of quartz, its

imbedded fragments (broken from the more solid parts of the mass, as it

rose, and enveloped by the softer parts), its concretionary nodules and

new minerals, etc.

"Beneath this, the granite which had been simply disintegrated was again

solidified, and returned in all respects to its former condition. The

temperature, however, and with it the expansive force of the inferior

zone, was continually on the increase, the caloric of the interior of

the globe still endeavoring to put itself in equilibrio by passing off

towards the less-intensely heated crust.

"This continually increasing expansive force must at length have

overcome the resistance opposed by the tenacity and weight of the

overlying consolidated strata. It is reasonable to suppose that this

result took place contemporaneously, or nearly so, on many spots,

wherever accidental circumstances in the texture or composition of the

oceanic deposits led them to yield more readily; and in this manner

were produced those original fissures in the primeval crust of the earth

through some of which (fissures of elevation) were intruded portions of

interior crystalline zones in a solid or nearly solid state, together

with more or less of the intumescent granite, in the manner

above described; while others (fissures of eruption) gave rise to

extravasations of the heated crystalline matter, in the form of

lavas--that is, still further liquefied by the greater comparative

reduction of the pressure they endured."(3)

The Neptunists stoutly contended for the aqueous origin of volcanic as

of other mountains. But the facts were with Scrope, and as time went

on it came to be admitted that not merely volcanoes, but many "trap"

formations not taking the form of craters, had been made by the

obtrusion of molten rock through fissures in overlying strata. Such,

for example, to cite familiar illustrations, are Mount Holyoke, in

Massachusetts, and the well-known formation of the Palisades along the

Hudson.

But to admit the "Plutonic" origin of such widespread formations was

practically to abandon the Neptunian hypothesis. So gradually the

Huttonian explanation of the origin of granites and other "igneous"

rocks, whether massed or in veins, came to be accepted. Most geologists

then came to think of the earth as a molten mass, on which the crust

rests as a mere film. Some, indeed, with Lyell, preferred to believe

that the molten areas exist only as lakes in a solid crust, heated to

melting, perhaps, by electrical or chemical action, as Davy suggested.

More recently a popular theory attempts to reconcile geological facts

with the claim of the physicists, that the earth's entire mass is at

least as rigid as steel, by supposing that a molten film rests between

the observed solid crust and the alleged solid nucleus. But be that

as it may, the theory that subterranean heat has been instrumental in

determining the condition of "primary" rocks, and in producing many

other phenomena of the earth's crust, has never been in dispute since

the long controversy between the Neptunists and the Plutonists led to

its establishment.

LYELL AND UNIFORMITARIANISM

If molten matter exists beneath the crust of the earth, it must contract

in cooling, and in so doing it must disturb the level of the portion of

the crust already solidified. So a plausible explanation of the upheaval

of continents and mountains was supplied by the Plutonian theory, as

Hutton had from the first alleged. But now an important difference

of opinion arose as to the exact rationale of such upheavals. Hutton

himself, and practically every one else who accepted his theory, had

supposed that there are long periods of relative repose, during which

the level of the crust is undisturbed, followed by short periods of

active stress, when continents are thrown up with volcanic suddenness,

as by the throes of a gigantic earthquake. But now came Charles Lyell

with his famous extension of the "uniformitarian" doctrine, claiming

that past changes of the earth's surface have been like present changes

in degree as well as in kind. The making of continents and mountains,

he said, is going on as rapidly to-day as at any time in the past. There

have been no gigantic cataclysmic upheavals at any time, but all

changes in level of the strata as a whole have been gradual, by slow

oscillation, or at most by repeated earthquake shocks such as are still

often experienced.

In support of this very startling contention Lyell gathered a mass

of evidence of the recent changes in level of continental areas. He

corroborated by personal inspection the claim which had been made by

Playfair in 1802, and by Von Buch in 1807, that the coast-line of Sweden

is rising at the rate of from a few inches to several feet in a

century. He cited Darwin's observations going to prove that Patagonia is

similarly rising, and Pingel's claim that Greenland is slowly sinking.

Proof as to sudden changes of level of several feet, over large areas,

due to earthquakes, was brought forward in abundance. Cumulative

evidence left it no longer open to question that such oscillatory

changes of level, either upward or downward, are quite the rule, and

it could not be denied that these observed changes, if continued long

enough in one direction, would produce the highest elevations. The

possibility that the making of even the highest ranges of mountains had

been accomplished without exaggerated catastrophic action came to be

freely admitted.

It became clear that the supposedly stable-land surfaces are in

reality much more variable than the surface of the "shifting sea"; that

continental masses, seemingly so fixed, are really rising and falling

in billows thousands of feet in height, ages instead of moments being

consumed in the sweep between crest and hollow.

These slow oscillations of land surfaces being understood, many

geological enigmas were made clear--such as the alternation of marine

and fresh-water formations in a vertical series, which Cuvier and

Brongniart had observed near Paris; or the sandwiching of layers of

coal, of subaerial formation, between layers of subaqueous clay or

sandstone, which may be observed everywhere in the coal measures. In

particular, the extreme thickness of the sedimentary strata as a whole,

many times exceeding the depth of the deepest known sea, was for the

first time explicable when it was understood that such strata had formed

in slowly sinking ocean-beds.

All doubt as to the mode of origin of stratified rocks being thus

removed, the way was opened for a more favorable consideration of

that other Huttonian doctrine of the extremely slow denudation of land

surfaces. The enormous amount of land erosion will be patent to any

one who uses his eyes intelligently in a mountain district. It will be

evident in any region where the strata are tilted--as, for example, the

Alleghanies--that great folds of strata which must once have risen miles

in height have in many cases been worn entirely away, so that now a

valley marks the location of the former eminence. Where the strata are

level, as in the case of the mountains of Sicily, the Scotch Highlands,

and the familiar Catskills, the evidence of denudation is, if possible,

even more marked; for here it is clear that elevation and valley have

been carved by the elements out of land that rose from the sea as level

plateaus.

But that this herculean labor of land-sculpturing could have been

accomplished by the slow action of wind and frost and shower was an

idea few men could grasp within the first half-century after Hutton

propounded it; nor did it begin to gain general currency until Lyell's

crusade against catastrophism, begun about 1830, had for a quarter of a

century accustomed geologists to the thought of slow, continuous changes

producing final results of colossal proportions. And even long after

that it was combated by such men as Murchison, Director-General of

the Geological Survey of Great Britain, then accounted the foremost

field-geologist of his time, who continued to believe that the existing

valleys owe their main features to subterranean forces of upheaval.

Even Murchison, however, made some recession from the belief of the

Continental authorities, Elie de Beaumont and Leopold von Buch,

who contended that the mountains had sprung up like veritable

jacks-in-the-box. Von Buch, whom his friend and fellow-pupil Von

Humboldt considered the foremost geologist of the time, died in 1853,

still firm in his early faith that the erratic bowlders found high on

the Jura had been hurled there, like cannon-balls, across the valley of

Geneva by the sudden upheaval of a neighboring mountain-range.

AGASSIZ AND THE GLACIAL THEORY

The bowlders whose presence on the crags of the Jura the old Gerinan

accounted for in a manner so theatrical had long been a source of

contention among geologists. They are found not merely on the Jura,

but on numberless other mountains in all north-temperate latitudes, and

often far out in the open country, as many a farmer who has broken his

plough against them might testify. The early geologists accounted for

them, as for nearly everything else, with their supposititious Deluge.

Brongniart and Cuvier and Buckland and their contemporaries appeared

to have no difficulty in conceiving that masses of granite weighing

hundreds of tons had been swept by this current scores or hundreds

of miles from their source. But, of course, the uniformitarian faith

permitted no such explanation, nor could it countenance the projection

idea; so Lyell was bound to find some other means of transportation for

the puzzling erratics.

The only available medium was ice, but, fortunately, this one seemed

quite sufficient. Icebergs, said Lyell, are observed to carry all manner

of debris, and deposit it in the sea-bottoms. Present land surfaces

have often been submerged beneath the sea. During the latest of these

submergences icebergs deposited the bowlders now scattered here

and there over the land. Nothing could be simpler or more clearly

uniformitarian. And even the catastrophists, though they met Lyell

amicably on almost no other theoretical ground, were inclined to admit

the plausibility of his theory of erratics. Indeed, of all Lyell's

nonconformist doctrines, this seemed the one most likely to meet with

general acceptance.

Yet, even as this iceberg theory loomed large and larger before the

geological world, observations were making in a different field that

were destined to show its fallacy. As early as 1815 a sharp-eyed

chamois-hunter of the Alps, Perraudin by name, had noted the existence

of the erratics, and, unlike most of his companion hunters, had puzzled

his head as to how the bowlders got where he saw them. He knew nothing

of submerged continents or of icebergs, still less of upheaving

mountains; and though he doubtless had heard of the Flood, he had no

experience of heavy rocks floating like corks in water. Moreover, he

had never observed stones rolling uphill and perching themselves on

mountain-tops, and he was a good enough uniformitarian (though he would

have been puzzled indeed had any one told him so) to disbelieve that

stones in past times had disported themselves differently in this regard

from stones of the present. Yet there the stones are. How did they get

there?

The mountaineer thought that he could answer that question. He saw about

him those gigantic serpent-like streams of ice called glaciers, "from

their far fountains slow rolling on," carrying with them blocks of

granite and other debris to form moraine deposits. If these glaciers had

once been much more extensive than they now are, they might have carried

the bowlders and left them where we find them. On the other hand, no

other natural agency within the sphere of the chamois-hunter's knowledge

could have accomplished this, ergo the glaciers must once have been more

extensive. Perraudin would probably have said that common-sense drove

him to this conclusion; but be that as it may, he had conceived one of

the few truly original and novel ideas of which the nineteenth century

can boast.

Perraudin announced his idea to the greatest scientist in his little

world--Jean de Charpentier, director of the mines at Bex, a skilled

geologist who had been a fellow-pupil of Von Buch and Von Humboldt

under Werner at the Freiberg School of Mines. Charpentier laughed at

the mountaineer's grotesque idea, and thought no more about it. And ten

years elapsed before Perraudin could find any one who treated his notion

with greater respect. Then he found a listener in M. Venetz, a civil

engineer, who read a paper on the novel glacial theory before a local

society in 1823. This brought the matter once more to the attention of

De Charpentier, who now felt that there might be something in it worth

investigation.

A survey of the field in the light of the new theory soon convinced

Charpentier that the chamois-hunter had all along been right. He became

an enthusiastic supporter of the idea that the Alps had once been

imbedded in a mass of ice, and in 1836 he brought the notion to the

attention of Louis Agassiz, who was spending the summer in the Alps.

Agassiz was sceptical at first, but soon became a convert.

In 1840 Agassiz published a paper in which the results of his Alpine

studies were elaborated.

"Let us consider," he says, "those more considerable changes to which

glaciers are subject, or rather, the immense extent which they had in

the prehistoric period. This former immense extension, greater than any

that tradition has preserved, is proved, in the case of nearly every

valley in the Alps, by facts which are both many and well established.

The study of these facts is even easy if the student is looking out for

them, and if he will seize the least indication of their presence; and,

if it were a long time before they were observed and connected with

glacial action, it is because the evidences are often isolated and occur

at places more or less removed from the glacier which originated them.

If it be true that it is the prerogative of the scientific observer to

group in the field of his mental vision those facts which appear to be

without connection to the vulgar herd, it is, above all, in such a case

as this that he is called upon to do so. I have often compared these

feeble effects, produced by the glacial action of former ages, with the

appearance of the markings upon a lithographic stone, prepared for the

purpose of preservation, and upon which one cannot see the lines of the

draughtsman's work unless it is known beforehand where and how to search

for them.

"The fact of the former existence of glaciers which have now disappeared

is proved by the survival of the various phenomena which always

accompany them, and which continue to exist even after the ice has

melted. These phenomena are as follows:

"1. Moraines.--The disposition and composition of moraines enable them

to be always recognized, even when they are no longer adjacent to a

glacier nor immediately surround its lower extremities. I may remark

that lateral and terminal moraines alone enable us to recognize with

certainty the limits of glacial extension, because they can be easily

distinguished from the dikes and irregularly distributed stones carried

down by the Alpine torrents, The lateral moraines deposited upon the

sides of valleys are rarely affected by the larger torrents, but they

are, however, often cut by the small streams which fall down the side of

a mountain, and which, by interfering with their continuity, make them

so much more difficult to recognize.

"2. The Perched Bowlders.--It often happens that glaciers encounter

projecting points of rock, the sides of which become rounded, and around

which funnel-like cavities are formed with more or less profundity. When

glaciers diminish and retire, the blocks which have fallen into these

funnels often remain perched upon the top of the projecting rocky point

within it, in such a state of equilibrium that any idea of a current of

water as the cause of their transportation is completely inadmissible

on account of their position. When such points of rock project above

the surface of the glacier or appear as a more considerable islet in

the midst of its mass (such as is the case in the Jardin of the Mer de

Glace, above Montavert), such projections become surrounded on all

sides by stones which ultimately form a sort of crown around the summit

whenever the glaciers decrease or retire completely. Water currents

never produce anything like this; but, on the contrary, whenever a

stream breaks itself against a projecting rock, the stones which it

carries down are turned aside and form a more or less regular trail.

Never, under such circumstances, can the stones remain either at the

top or at the sides of the rock, for, if such a thing were possible,

the rapidity of the current would be accelerated by the increased

resistance, and the moving bowlders would be carried beyond the

obstruction before they were finally deposited.

"3. The polished and striated rocks, such as have been described in

Chapter XIV., afford yet further evidence of the presence of a glacier;

for, as has been said already, neither a current nor the action of waves

upon an extensive beach produces such effects. The general direction of

the channels and furrows indicates the direction of the general movement

of the glacier, and the streaks which vary more or less from this

direction are produced by the local effects of oscillation and retreat,

as we shall presently see.

"4. The Lapiaz, or Lapiz, which the inhabitants of German Switzerland

call Karrenfelder, cannot always be distinguished from erosions,

because, both produced as they are by water, they do not differ in their

exterior characteristics, but only in their positions. Erosions due to

torrents are always found in places more or less depressed, and never

occur upon large inclined surfaces. The Lapiaz, on the contrary, are

frequently found upon the projecting parts of the sides of valleys in

places where it is not possible to suppose that water has ever formed

a current. Some geologists, in their embarrassment to explain these

phenomena, have supposed that they were due to the infiltration of

acidulated water, but this hypothesis is purely gratuitous.

"We will now describe the remains of these various phenomena as they are

found in the Alps outside the actual glacial limits, in order to prove

that at a certain epoch glaciers were much larger than they are to-day.

"The ancient moraines, situated as they are at a great distance from

those of the present day, are nowhere so distinct or so frequent as

in Valais, where MM. Venetz and J. de Charpentier noticed them for the

first time; but as their observations are as yet unpublished, and they

themselves gave me the information, it would be an appropriation of

their discovery if I were to describe them here in detail. I will limit

myself to say that there can be found traces, more or less distinct, of

ancient terminal moraines in the form of vaulted dikes at the foot of

every glacier, at a distance of a few minutes' walk, a quarter of an

hour, a half-hour, an hour, and even of several leagues from their

present extremities. These traces become less distinct in proportion

to their distance from the glacier, and, since they are also often

traversed by torrents, they are not as continuous as the moraines which

are nearer to the glaciers. The farther these ancient moraines are

removed from the termination of a glacier, the higher up they reach upon

the sides of the valley, which proves to us that the thickness of the

glacier must have been greater when its size was larger. At the same

time, their number indicates so many stopping-places in the retreat of

the glacier, or so many extreme limits of its extension--limits which

were never reached again after it had retired. I insist upon this point,

because if it is true that all these moraines demonstrate a larger

extent of the glacier, they also prove that their retreat into their

present boundaries, far from having been catastrophic, was marked on the

contrary by periods of repose more or less frequent, which caused the

formation of a series of concentric moraines which even now indicate

their retrogression.

"The remains of longitudinal moraines are less frequent, less distinct,

and more difficult to investigate, because, indicating as they do the

levels to which the edges of the glacier reached at different epochs,

it is generally necessary to look for them above the line of the

paths along the escarpments of the valleys, and hence it is not always

possible to follow them along a valley. Often, also, the sides of a

valley which enclosed a glacier are so steep that it is only here and

there that the stones have remained in place. They are, nevertheless,

very distinct in the lower part of the valley of the Rhone, between

Martigny and the Lake of Geneva, where several parallel ridges can be

observed, one above the other, at a height of one thousand, one thousand

two hundred, and even one thousand five hundred feet above the Rhone.

It is between St. Maurice and the cascade of Pissevache, close to the

hamlet of Chaux-Fleurie, that they are most accessible, for at this

place the sides of the valley at different levels ascend in little

terraces, upon which the moraines have been preserved. They are also

very distinct above the Bains de Lavey, and above the village of Monthey

at the entrance of the Val d'Illiers, where the sides of the valley are

less inclined than in many other places.

"The perched bowlders which are found in the Alpine valleys, at

considerable distances from the glaciers, occupy at times positions so

extraordinary that they excite in a high degree the curiosity of those

who see them. For instance, when one sees an angular stone perched upon

the top of an isolated pyramid, or resting in some way in a very steep

locality, the first inquiry of the mind is, When and how have these

stones been placed in such positions, where the least shock would seem

to turn them over? But this phenomenon is not in the least astonishing

when it is seen to occur also within the limits of actual glaciers, and

it is recalled by what circumstances it is occasioned.

"The most curious examples of perched stones which can be cited are

those which command the northern part of the cascade of Pissevache,

close to Chaux-Fleurie, and those above the Bains de Lavey, close to the

village of Morcles; and those, even more curious, which I have seen in

the valley of St. Nicolas and Oberhasli. At Kirchet, near Meiringen, can

be seen some very remarkable crowns of bowlders around several domes

of rock which appear to have been projected above the surface of the

glacier which surrounded them. Something very similar can be seen around

the top of the rock of St. Triphon.

"The extraordinary phenomenon of perched stones could not escape the

observing eye of De Saussure, who noticed several at Saleve, of which

he described the positions in the following manner: 'One sees,' said he,

'upon the slope of an inclined meadow, two of these great bowlders of

granite, elevated one upon the other, above the grass at a height of two

or three feet, upon a base of limestone rock on which both rest. This

base is a continuation of the horizontal strata of the mountain, and is

even united with it visibly on its lower face, being cut perpendicularly

upon the other sides, and is not larger than the stone which it

supports.' But seeing that the entire mountain is composed of the same

limestone, De Saussure naturally concluded that it would be absurd to

think that it was elevated precisely and only beneath the blocks of

granite. But, on the other hand, since he did not know the manner in

which these perched stones are deposited in our days by glacial action,

he had recourse to another explanation: He supposes that the rock was

worn away around its base by the continual erosion of water and air,

while the portion of the rock which served as the base for the granite

had been protected by it. This explanation, although very ingenious,

could no longer be admitted after the researches of M. Elie de Beaumont

had proved that the action of atmospheric agencies was not by a good

deal so destructive as was theretofore supposed. De Saussure speaks

also of a detached bowlder, situated upon the opposite side of the

Tete-Noire, 'which is,' he says, 'of so great a size that one is tempted

to believe that it was formed in the place it occupies; and it is called

Barme russe, because it is worn away beneath in the form of a cave which

can afford accommodation for more than thirty persons at a time."(4)

But the implications of the theory of glaciers extend, so Agassiz has

come to believe, far beyond the Alps. If the Alps had been covered with

an ice sheet, so had many other regions of the northern hemisphere.

Casting abroad for evidences of glacial action, Agassiz found them

everywhere in the form of transported erratics, scratched and polished

outcropping rocks, and moraine-like deposits. Finally, he became

convinced that the ice sheet that covered the Alps had spread over the

whole of the higher latitudes of the northern hemisphere, forming an

ice cap over the globe. Thus the common-sense induction of the

chamois-hunter blossomed in the mind of Agassiz into the conception of a

universal ice age.

In 1837 Agassiz had introduced his theory to the world, in a paper read

at Neuchatel, and three years later he published his famous Etudes sur

les Glaciers, from which we have just quoted. Never did idea make a more

profound disturbance in the scientific world. Von Buch treated it

with alternate ridicule, contempt, and rage; Murchison opposed it with

customary vigor; even Lyell, whose most remarkable mental endowment was

an unfailing receptiveness to new truths, could not at once discard

his iceberg theory in favor of the new claimant. Dr. Buckland, however,

after Agassiz had shown him evidence of former glacial action in his own

Scotland, became a convert--the more readily, perhaps, as it seemed to

him to oppose the uniformitarian idea. Gradually others fell in line,

and after the usual imbittered controversy and the inevitable full

generation of probation, the idea of an ice age took its place among

the accepted tenets of geology. All manner of moot points still demanded

attention--the cause of the ice age, the exact extent of the ice sheet,

the precise manner in which it produced its effects, and the exact

nature of these effects; and not all of these have even yet been

determined. But, details aside, the ice age now has full recognition

from geologists as an historical period. There may have been many ice

ages, as Dr. Croll contends; there was surely one; and the conception

of such a period is one of the very few ideas of our century that no

previous century had even so much as faintly adumbrated.

THE GEOLOGICAL AGES

But, for that matter, the entire subject of historical geology is

one that had but the barest beginning before our century. Until the

paleontologist found out the key to the earth's chronology, no one--not

even Hutton--could have any definite idea as to the true story of the

earth's past. The only conspicuous attempt to classify the strata was

that made by Werner, who divided the rocks into three systems, based on

their supposed order of deposition, and called primary, transition, and

secondary.

Though Werner's observations were confined to the small province of

Saxony, he did not hesitate to affirm that all over the world the

succession of strata would be found the same as there, the concentric

layers, according to this conception, being arranged about the earth

with the regularity of layers on an onion. But in this Werner was

as mistaken as in his theoretical explanation of the origin of the

"primary" rocks. It required but little observation to show that the

exact succession of strata is never precisely the same in any widely

separated regions. Nevertheless, there was a germ of truth in Werner's

system. It contained the idea, however faultily interpreted, of a

chronological succession of strata; and it furnished a working outline

for the observers who were to make out the true story of geological

development. But the correct interpretation of the observed facts could

only be made after the Huttonian view as to the origin of strata had

gained complete acceptance.

When William Smith, having found the true key to this story, attempted

to apply it, the territory with which he had to deal chanced to be one

where the surface rocks are of that later series which Werner termed

secondary. He made numerous subdivisions within this system, based

mainly on the fossils. Meantime it was found that, judged by the

fossils, the strata that Brongniart and Cuvier studied near Paris were

of a still more recent period (presumed at first to be due to the latest

deluge), which came to be spoken of as tertiary. It was in these beds,

some of which seemed to have been formed in fresh-water lakes, that many

of the strange mammals which Cuvier first described were found.

But the "transition" rocks, underlying the "secondary" system that Smith

studied, were still practically unexplored when, along in the thirties,

they were taken in hand by Roderick Impey Murchison, the reformed

fox-hunter and ex-captain, who had turned geologist to such notable

advantage, and Adam Sedgwick, the brilliant Woodwardian professor at

Cambridge.

Working together, these two friends classified the

transition rocks into chronological groups, since familiar to every one

in the larger outlines as the Silurian system (age of invertebrates) and

the Devonian system (age of fishes)--names derived respectively from the

country of the ancient Silures, in Wales and Devonshire, England. It

was subsequently discovered that these systems of strata, which crop out

from beneath newer rocks in restricted areas in Britain, are spread out

into broad, undisturbed sheets over thousands of miles in continental

Europe and in America. Later on Murchison studied them in Russia,

and described them, conjointly with Verneuil and Von Kerserling, in

a ponderous and classical work. In America they were studied by Hall,

Newberry, Whitney, Dana, Whitfield, and other pioneer geologists, who

all but anticipated their English contemporaries.

The rocks that are of still older formation than those studied by

Murchison and Sedgwick (corresponding in location to the "primary" rocks

of Werner's conception) are the surface feature of vast areas in Canada,

and were first prominently studied there by William I. Logan, of the

Canadian Government Survey, as early as 1846, and later on by Sir

William Dawson. These rocks--comprising the Laurentian system--were

formerly supposed to represent parts of the original crust of the earth,

formed on first cooling from a molten state; but they are now more

generally regarded as once-stratified deposits metamorphosed by the

action of heat.

Whether "primitive" or metamorphic, however, these Canadian rocks, and

analogous ones beneath the fossiliferous strata of other countries,

are the oldest portions of the earth's crust of which geology has any

present knowledge. Mountains of this formation, as the Adirondacks and

the Storm King range, overlooking the Hudson near West Point, are the

patriarchs of their kind, beside which Alleghanies and Sierra Nevadas

are recent upstarts, and Rockies, Alps, and Andes are mere parvenus of

yesterday.

The Laurentian rocks were at first spoken of as representing "Azoic"

time; but in 1846 Dawson found a formation deep in their midst which was

believed to b e the fossil relic of a very low form of life, and after

that it became customary to speak of the system as "Eozoic." Still more

recently the title of Dawson's supposed fossil to rank as such has been

questioned, and Dana's suggestion that the early rocks be termed merely

Archman has met with general favor. Murchison and Sedgwick's Silurian,

Devonian, and Carboniferous groups (the ages of invertebrates, of

fishes, and of coal plants, respectively) are together spoken of as

representing Paleozoic time. William Smith's system of strata, next

above these, once called "secondary," represents Mesozoic time, or

the age of reptiles. Still higher, or more recent, are Cuvier and

Brongniart's tertiary rocks, representing the age of mammals. Lastly,

the most recent formations, dating back, however, to a period far enough

from recent in any but a geological sense, are classed as quaternary,

representing the age of man.

It must not be supposed, however, that the successive "ages" of the

geologist are shut off from one another in any such arbitrary way as

this verbal classification might seem to suggest. In point of fact,

these "ages" have no better warrant for existence than have the

"centuries" and the "weeks" of every-day computation. They are

convenient, and they may even stand for local divisions in the strata,

but they are bounded by no actual gaps in the sweep of terrestrial

events.

Moreover, it must be understood that the "ages" of different continents,

though described under the same name, are not necessarily of exact

contemporaneity. There is no sure test available by which it could be

shown that the Devonian age, for instance, as outlined in the strata of

Europe, did not begin millions of years earlier or later than the period

whose records are said to represent the Devonian age in America. In

attempting to decide such details as this, mineralogical data fail us

utterly. Even in rocks of adjoining regions identity of structure is no

proof of contemporaneous origin; for the veritable substance of the

rock of one age is ground up to build the rocks of subsequent ages.

Furthermore, in seas where conditions change but little the same form

of rock may be made age after age. It is believed that chalk-beds still

forming in some of our present seas may form one continuous mass dating

back to earliest geologic ages. On the other hand, rocks different in

character maybe formed at the same time in regions not far apart--say

a sandstone along shore, a coral limestone farther seaward, and a

chalk-bed beyond. This continuous stratum, broken in the process of

upheaval, might seem the record of three different epochs.

Paleontology, of course, supplies far better chronological tests, but

even these have their limitations. There has been no time since rocks

now in existence were formed, if ever, when the earth had a uniform

climate and a single undiversified fauna over its entire land surface,

as the early paleontologists supposed. Speaking broadly, the same

general stages have attended the evolution of organic forms everywhere,

but there is nothing to show that equal periods of time witnessed

corresponding changes in diverse regions, but quite the contrary.

To cite but a single illustration, the marsupial order, which is the

dominant mammalian type of the living fauna of Australia to-day,

existed in Europe and died out there in the tertiary age. Hence a future

geologist might think the Australia of to-day contemporaneous with a

period in Europe which in reality antedated it by perhaps millions of

years.

All these puzzling features unite to render the subject of historical

geology anything but the simple matter the fathers of the science

esteemed it. No one would now attempt to trace the exact sequence of

formation of all the mountains of the globe, as Elie de Beaumont did

a half-century ago. Even within the limits of a single continent, the

geologist must proceed with much caution in attempting to chronicle the

order in which its various parts rose from the matrix of the sea. The

key to this story is found in the identification of the strata that

are the surface feature in each territory. If Devonian rocks are at

the surface in any given region, for example, it would appear that this

region became a land surface in the Devonian age, or just afterwards.

But a moment's consideration shows that there is an element of

uncertainty about this, due to the steady denudation that all land

surfaces undergo. The Devonian rocks may lie at the surface simply

because the thousands of feet of carboniferous strata that once lay

above them have been worn away. All that the cautious geologist dare

assert, therefore, is that the region in question did not become

permanent land surface earlier than the Devonian age.

But to know even this is much--sufficient, indeed, to establish the

chronological order of elevation, if not its exact period, for all parts

of any continent that have been geologically explored--understanding

always that there must be no scrupling about a latitude of a few

millions or perhaps tens of millions of years here and there.

Regarding our own continent, for example, we learn through the

researches of a multitude of workers that in the early day it was a mere

archipelago. Its chief island--the backbone of the future continent--was

a great V-shaped area surrounding what is now Hudson Bay, an area built

tip, perhaps, through denudation of a yet more ancient polar continent,

whose existence is only conjectured. To the southeast an island that

is now the Adirondack Mountains, and another that is now the Jersey

Highlands rose above the waste of waters, and far to the south stretched

probably a line of islands now represented by the Blue Ridge Mountains.

Far off to the westward another line of islands foreshadowed our present

Pacific border. A few minor islands in the interior completed the

archipelago.

From this bare skeleton the continent grew, partly by the deposit of

sediment from the denudation of the original islands (which once towered

miles, perhaps, where now they rise thousands of feet), but largely also

by the deposit of organic remains, especially in the interior sea, which

teemed with life. In the Silurian ages, invertebrates--brachiopods and

crinoids and cephalopods--were the dominant types. But very early--no

one knows just when--there came fishes of many strange forms, some of

the early ones enclosed in turtle-like shells. Later yet, large spaces

within the interior sea having risen to the surface, great marshes or

forests of strange types of vegetation grew and deposited their remains

to form coal-beds. Many times over such forests were formed, only to be

destroyed by the oscillations of the land surface. All told, the strata

of this Paleozoic period aggregate several miles in thickness, and the

time consumed in their formation stands to all later time up to the

present, according to Professor Dana's estimate, as three to one.

Towards the close of this Paleozoic era the Appalachian Mountains

were slowly upheaved in great convoluted folds, some of them probably

reaching three or four miles above the sea-level, though the tooth

of time has since gnawed them down to comparatively puny limits. The

continental areas thus enlarged were peopled during the ensuing Mesozoic

time with multitudes of strange reptiles, many of them gigantic in size.

The waters, too, still teeming with invertebrates and fishes, had their

quota of reptilian monsters; and in the air were flying reptiles, some

of which measured twenty-five feet from tip to tip of their batlike

wings. During this era the Sierra Nevada Mountains rose. Near the

eastern border of the forming continent the strata were perhaps now too

thick and stiff to bend into mountain folds, for they were rent into

great fissures, letting out floods of molten lava, remnants of which are

still in evidence after ages of denudation, as the Palisades along the

Hudson, and such elevations as Mount Holyoke in western Massachusetts.

Still there remained a vast interior sea, which later on, in the

tertiary age, was to be divided by the slow uprising of the land, which

only yesterday--that is to say, a million, or three or five or ten

million, years ago--became the Rocky Mountains. High and erect these

young mountains stand to this day, their sharp angles and rocky contours

vouching for their youth, in strange contrast with the shrunken forms

of the old Adirondacks, Green Mountains, and Appalachians, whose lowered

heads and rounded shoulders attest the weight of ages. In the vast lakes

which still remained on either side of the Rocky range, tertiary

strata were slowly formed to the ultimate depth of two or three miles,

enclosing here and there those vertebrate remains which were to be

exposed again to view by denudation when the land rose still higher,

and then, in our own time, to tell so wonderful a story to the

paleontologist.

Finally, the interior seas were filled, and the shore lines of the

continent assumed nearly their present outline.

Then came the long winter of the glacial epoch--perhaps of a succession

of glacial epochs. The ice sheet extended southward to about the

fortieth parallel, driving some animals before it, and destroying those

that were unable to migrate. At its fulness, the great ice mass lay

almost a mile in depth over New England, as attested by the scratched

and polished rock surfaces and deposited erratics in the White

Mountains. Such a mass presses down with a weight of about one hundred

and twenty-five tons to the square foot, according to Dr. Croll's

estimate. It crushed and ground everything beneath it more or less, and

in some regions planed off hilly surfaces into prairies. Creeping slowly

forward, it carried all manner of debris with it. When it melted away

its terminal moraine built up the nucleus of the land masses now known

as Long Island and Staten Island; other of its deposits formed the

"drumlins" about Boston famous as Bunker and Breed's hills; and it left

a long, irregular line of ridges of "till" or bowlder clay and scattered

erratics clear across the country at about the latitude of New York

city.

As the ice sheet slowly receded it left minor moraines all along its

course. Sometimes its deposits dammed up river courses or inequalities

in the surface, to form the lakes which everywhere abound over Northern

territories. Some glacialists even hold the view first suggested by

Ramsey, of the British Geological Survey, that the great glacial sheets

scooped out the basins of many lakes, including the system that feeds

the St. Lawrence. At all events, it left traces of its presence all

along the line of its retreat, and its remnants exist to this day as

mountain glaciers and the polar ice cap. Indeed, we live on the border

of the last glacial epoch, for with the closing of this period the long

geologic past merges into the present.

PAST, PRESENT, AND FUTURE

And the present, no less than the past, is a time of change. This is the

thought which James Hutton conceived more than a century ago, but which

his contemporaries and successors were so very slow to appreciate. Now,

however, it has become axiomatic--one can hardly realize that it was

ever doubted. Every new scientific truth, says Agassiz, must pass

through three stages--first, men say it is not true; then they declare

it hostile to religion; finally, they assert that every one has known

it always. Hutton's truth that natural law is changeless and eternal

has reached this final stage. Nowhere now could you find a scientist

who would dispute the truth of that text which Lyell, quoting from

Playfair's Illustrations of the Huttonian Theory, printed on the

title-page of his Principles: "Amid all the revolutions of the globe

the economy of Nature has been uniform, and her laws are the only things

that have resisted the general movement. The rivers and the rocks, the

seas and the continents, have been changed in all their parts; but

the laws which direct those changes, and the rules to which they are

subject, have remained invariably the same."

But, on the other hand, Hutton and Playfair, and in particular Lyell,

drew inferences from this principle which the modern physicist can by no

means admit. To them it implied that the changes on the surface of the

earth have always been the same in degree as well as in kind, and must

so continue while present forces hold their sway. In other words, they

thought of the world as a great perpetual-motion machine. But the

modern physicist, given truer mechanical insight by the doctrines of the

conservation and the dissipation of energy, will have none of that. Lord

Kelvin, in particular, has urged that in the periods of our earth's in

fancy and adolescence its developmental changes must have been, like

those of any other infant organism, vastly more rapid and pronounced

than those of a later day; and to every clear thinker this truth also

must now seem axiomatic.

Whoever thinks of the earth as a cooling globe can hardly doubt that its

crust, when thinner, may have heaved under strain of the moon's tidal

pull--whether or not that body was nearer--into great billows, daily

rising and falling, like waves of the present seas vastly magnified.

Under stress of that same lateral pressure from contraction which now

produces the slow depression of the Jersey coast, the slow rise of

Sweden, the occasional belching of an insignificant volcano, the jetting

of a geyser, or the trembling of an earthquake, once large areas were

rent in twain, and vast floods of lava flowed over thousands of square

miles of the earth's surface, perhaps, at a single jet; and, for aught

we know to the contrary, gigantic mountains may have heaped up their

contorted heads in cataclysms as spasmodic as even the most ardent

catastrophist of the elder day of geology could have imagined.

The atmosphere of that early day, filled with vast volumes of carbon,

oxygen, and other chemicals that have since been stored in beds of coal,

limestone, and granites, may have worn down the rocks on the one hand

and built up organic forms on the other, with a rapidity that would now

seem hardly conceivable.

And yet while all these anomalous things went on, the same laws held

sway that now are operative; and a true doctrine of uniformitarianism

would make no unwonted concession in conceding them all--though most of

the imbittered geological controversies of the middle of the nineteenth

century were due to the failure of both parties to realize that simple

fact.

And as of the past and present, so of the future. The same forces will

continue to operate; and under operation of these unchanging forces each

day will differ from every one that has preceded it. If it be true,

as every physicist believes, that the earth is a cooling globe, then,

whatever its present stage of refrigeration, the time must come when its

surface contour will assume a rigidity of level not yet attained. Then,

just as surely, the slow action of the elements will continue to wear

away the land surfaces, particle by particle, and transport them to the

ocean, as it does to-day, until, compensation no longer being afforded

by the upheaval of the continents, the last foot of dry land will sink

for the last time beneath the water, the last mountain-peak melting

away, and our globe, lapsing like any other organism into its second

childhood, will be on the surface--as presumably it was before the first

continent rose--one vast "waste of waters." As puny man conceives time

and things, an awful cycle will have lapsed; in the sweep of the cosmic

life, a pulse-beat will have throbbed.

V. THE NEW SCIENCE OF METEOROLOGY

METEORITES

"An astonishing miracle has just occurred in our district," wrote M.

Marais, a worthy if undistinguished citizen of France, from his home at

L'Aigle, under date of "the 13th Floreal, year 11"--a date which outside

of France would be interpreted as meaning May 3, 1803. This "miracle"

was the appearance of a "fireball" in broad daylight--"perhaps it was

wildfire," says the naive chronicle--which "hung over the meadow," being

seen by many people, and then exploded with a loud sound, scattering

thousands of stony fragments over the surface of a territory some miles

in extent.

Such a "miracle" could not have been announced at a more opportune time.

For some years the scientific world had been agog over the question

whether such a form of lightning as that reported--appearing in a clear

sky, and hurling literal thunderbolts--had real existence. Such

cases had been reported often enough, it is true. The "thunderbolts"

themselves were exhibited as sacred relics before many an altar, and

those who doubted their authenticity had been chided as having "an

evil heart of unbelief." But scientific scepticism had questioned the

evidence, and late in the eighteenth century a consensus of opinion

in the French Academy had declined to admit that such stones had been

"conveyed to the earth by lightning," let alone any more miraculous

agency.

In 1802, however, Edward Howard had read a paper before the Royal

Society in which, after reviewing the evidence recently put forward,

he had reached the conclusion that the fall of stones from the sky,

sometimes or always accompanied by lightning, must be admitted as

an actual phenomenon, however inexplicable. So now, when the great

stone-fall at L'Aigle was announced, the French Academy made haste to

send the brilliant young physicist Jean Baptiste Biot to investigate

it, that the matter might, if possible, be set finally at rest.

The investigation was in all respects successful, and Biot's report

transferred the stony or metallic lightning-bolt--the aerolite or

meteorite--from the realm of tradition and conjecture to that of

accepted science.

But how explain this strange phenomenon? At once speculation was rife.

One theory contended that the stony masses had not actually fallen, but

had been formed from the earth by the action of the lightning; but this

contention was early abandoned. The chemists were disposed to believe

that the aerolites had been formed by the combination of elements

floating in the upper atmosphere. Geologists, on the other hand, thought

them of terrestrial origin, urging that they might have been thrown up

by volcanoes. The astronomers, as represented by Olbers and Laplace,

modified this theory by suggesting that the stones might, indeed, have

been cast out by volcanoes, but by volcanoes situated not on the earth,

but on the moon.

And one speculator of the time took a step even more daring, urging that

the aerolites were neither of telluric nor selenitic origin, nor yet

children of the sun, as the old Greeks had, many of them, contended,

but that they are visitants from the depths of cosmic space. This bold

speculator was the distinguished German physicist Ernst F. F. Chladni,

a man of no small repute in his day. As early as 1794 he urged his

cosmical theory of meteorites, when the very existence of meteorites was

denied by most scientists. And he did more: he declared his belief

that these falling stones were really one in origin and kind with those

flashing meteors of the upper atmosphere which are familiar everywhere

as "shooting-stars."

Each of these coruscating meteors, he affirmed, must tell of the

ignition of a bit of cosmic matter entering the earth's atmosphere. Such

wandering bits of matter might be the fragments of shattered worlds, or,

as Chladni thought more probable, merely aggregations of "world stuff"

never hitherto connected with any large planetary mass.

Naturally enough, so unique a view met with very scant favor.

Astronomers at that time saw little to justify it; and the

non-scientific world rejected it with fervor as being "atheistic and

heretical," because its acceptance would seem to imply that the universe

is not a perfect mechanism.

Some light was thrown on the moot point presently by the observations of

Brandes and Benzenberg, which tended to show that falling-stars travel

at an actual speed of from fifteen to ninety miles a second. This

observation tended to discredit the selenitic theory, since an object,

in order to acquire such speed in falling merely from the moon, must

have been projected with an initial velocity not conceivably to be given

by any lunar volcanic impulse. Moreover, there was a growing conviction

that there are no active volcanoes on the moon, and other considerations

of the same tenor led to the complete abandonment of the selenitic

theory.

But the theory of telluric origin of aerolites was by no means so easily

disposed of. This was an epoch when electrical phenomena were exciting

unbounded and universal interest, and there was a not unnatural tendency

to appeal to electricity in explanation of every obscure phenomenon; and

in this case the seeming similarity between a lightning flash and the

flash of an aerolite lent color to the explanation. So we find Thomas

Forster, a meteorologist of repute, still adhering to the atmospheric

theory of formation of aerolites in his book published in 1823; and,

indeed, the prevailing opinion of the time seemed divided between

various telluric theories, to the neglect of any cosmical theory

whatever.

But in 1833 occurred a phenomenon which set the matter finally at

rest. A great meteoric shower occurred in November of that year, and

in observing it Professor Denison Olmstead, of Yale, noted that all

the stars of the shower appeared to come from a single centre or

vanishing-point in the heavens, and that this centre shifted its

position with the stars, and hence was not telluric. The full

significance of this observation was at once recognized by astronomers;

it demonstrated beyond all cavil the cosmical origin of the

shooting-stars. Some conservative meteorologists kept up the argument

for the telluric origin for some decades to come, as a matter of

course--such a band trails always in the rear of progress. But even

these doubters were silenced when the great shower of shooting-stars

appeared again in 1866, as predicted by Olbers and Newton, radiating

from the same point of the heavens as before.

Since then the spectroscope has added its confirmatory evidence as to

the identity of meteorite and shooting-star, and, moreover, has linked

these atmospheric meteors with such distant cosmic residents as comets

and nebulae. Thus it appears that Chladni's daring hypothesis of

1794 has been more than verified, and that the fragments of matter

dissociated from planetary connection--which be postulated and was

declared atheistic for postulating--have been shown to be billions

of times more numerous than any larger cosmic bodies of which we have

cognizance--so widely does the existing universe differ from man's

preconceived notions as to what it should be.

Thus also the "miracle" of the falling stone, against which the

scientific scepticism of yesterday presented "an evil heart of

unbelief," turns out to be the most natural phenomena, inasmuch as it is

repeated in our atmosphere some millions of times each day.

THE AURORA BOREALIS

If fire-balls were thought miraculous and portentous in days of yore,

what interpretation must needs have been put upon that vastly more

picturesque phenomenon, the aurora? "Through all the city," says the

Book of Maccabees, "for the space of almost forty days, there were seen

horsemen running in the air, in cloth of gold, armed with lances, like

a band of soldiers: and troops of horsemen in array encountering and

running one against another, with shaking of shields and multitude of

pikes, and drawing of swords, and casting of darts, and glittering of

golden ornaments and harness." Dire omens these; and hardly less ominous

the aurora seemed to all succeeding generations that observed it down

well into the eighteenth century--as witness the popular excitement in

England in 1716 over the brilliant aurora of that year, which became

famous through Halley's description.

But after 1752, when Franklin dethroned the lightning, all spectacular

meteors came to be regarded as natural phenomena, the aurora among the

rest. Franklin explained the aurora--which was seen commonly enough in

the eighteenth century, though only recorded once in the seventeenth--as

due to the accumulation of electricity on the surface of polar snows,

and its discharge to the equator through the upper atmosphere. Erasmus

Darwin suggested that the luminosity might be due to the ignition of

hydrogen, which was supposed by many philosophers to form the upper

atmosphere. Dalton, who first measured the height of the aurora,

estimating it at about one hundred miles, thought the phenomenon due

to magnetism acting on ferruginous particles in the air, and his

explanation was perhaps the most popular one at the beginning of the

last century.

Since then a multitude of observers have studied the aurora, but the

scientific grasp has found it as elusive in fact as it seems to casual

observation, and its exact nature is as undetermined to-day as it was a

hundred years ago. There has been no dearth of theories concerning it,

however. Blot, who studied it in the Shetland Islands in 1817, thought

it due to electrified ferruginous dust, the origin of which he ascribed

to Icelandic volcanoes. Much more recently the idea of ferruginous

particles has been revived, their presence being ascribed not to

volcanoes, but to the meteorites constantly being dissipated in the

upper atmosphere. Ferruginous dust, presumably of such origin, has been

found on the polar snows, as well as on the snows of mountain-tops, but

whether it could produce the phenomena of auroras is at least an open

question.

Other theorists have explained the aurora as due to the accumulation of

electricity on clouds or on spicules of ice in the upper air. Yet others

think it due merely to the passage of electricity through rarefied air

itself. Humboldt considered the matter settled in yet another way when

Faraday showed, in 1831, that magnetism may produce luminous effects.

But perhaps the prevailing theory of to-day assumes that the aurora is

due to a current of electricity generated at the equator and passing

through upper regions of space, to enter the earth at the magnetic

poles--simply reversing the course which Franklin assumed.

The similarity of the auroral light to that generated in a vacuum

bulb by the passage of electricity lends support to the long-standing

supposition that the aurora is of electrical origin, but the subject

still awaits complete elucidation. For once even that mystery-solver the

spectroscope has been baffled, for the line it sifts from the aurora is

not matched by that of any recognized substance. A like line is found

in the zodiacal light, it is true, but this is of little aid, for the

zodiacal light, though thought by some astronomers to be due to meteor

swarms about the sun, is held to be, on the whole, as mysterious as the

aurora itself.

Whatever the exact nature of the aurora, it has long been known to

be intimately associated with the phenomena of terrestrial magnetism.

Whenever a brilliant aurora is visible, the world is sure to be visited

with what Humboldt called a magnetic storm--a "storm" which manifests

itself to human senses in no way whatsoever except by deflecting the

magnetic needle and conjuring with the electric wire. Such magnetic

storms are curiously associated also with spots on the sun--just how no

one has explained, though the fact itself is unquestioned. Sun-spots,

too, seem directly linked with auroras, each of these phenomena passing

through periods of greatest and least frequency in corresponding cycles

of about eleven years' duration.

It was suspected a full century ago by Herschel that the variations in

the number of sun-spots had a direct effect upon terrestrial weather,

and he attempted to demonstrate it by using the price of wheat as a

criterion of climatic conditions, meantime making careful observation

of the sun-spots. Nothing very definite came of his efforts in this

direction, the subject being far too complex to be determined without

long periods of observation. Latterly, however, meteorologists,

particularly in the tropics, are disposed to think they find evidence

of some such connection between sun-spots and the weather as Herschel

suspected. Indeed, Mr. Meldrum declares that there is a positive

coincidence between periods of numerous sun-spots and seasons of

excessive rain in India.

That some such connection does exist seems intrinsically probable. But

the modern meteorologist, learning wisdom of the past, is extremely

cautious about ascribing casual effects to astronomical phenomena.

He finds it hard to forget that until recently all manner of climatic

conditions were associated with phases of the moon; that not so very

long ago showers of falling-stars were considered "prognostic" of

certain kinds of weather; and that the "equinoctial storm" had

been accepted as a verity by every one, until the unfeeling hand of

statistics banished it from the earth.

Yet, on the other hand, it is easily within the possibilities that the

science of the future may reveal associations between the weather and

sun-spots, auroras, and terrestrial magnetism that as yet are hardly

dreamed of. Until such time, however, these phenomena must feel

themselves very grudgingly admitted to the inner circle of meteorology.

More and more this science concerns itself, in our age of concentration

and specialization, with weather and climate. Its votaries no

longer concern themselves with stars or planets or comets or

shooting-stars--once thought the very essence of guides to weather

wisdom; and they are even looking askance at the moon, and asking her

to show cause why she also should not be excluded from their domain.

Equally little do they care for the interior of the earth, since they

have learned that the central emanations of heat which Mairan imagined

as a main source of aerial warmth can claim no such distinction. Even

such problems as why the magnetic pole does not coincide with the

geographical, and why the force of terrestrial magnetism decreases from

the magnetic poles to the magnetic equator, as Humboldt first discovered

that it does, excite them only to lukewarm interest; for magnetism,

they say, is not known to have any connection whatever with climate or

weather.

EVAPORATION, CLOUD FORMATION, AND DEW

There is at least one form of meteor, however, of those that interested

our forebears whose meteorological importance they did not overestimate.

This is the vapor of water. How great was the interest in this familiar

meteor at the beginning of the century is attested by the number of

theories then extant regarding it; and these conflicting theories bear

witness also to the difficulty with which the familiar phenomenon of the

evaporation of water was explained.

Franklin had suggested that air dissolves water much as water dissolves

salt, and this theory was still popular, though Deluc had disproved it

by showing that water evaporates even more rapidly in a vacuum than

in air. Deluc's own theory, borrowed from earlier chemists, was that

evaporation is the chemical union of particles of water with particles

of the supposititious element heat. Erasmus Darwin combined the two

theories, suggesting that the air might hold a variable quantity of

vapor in mere solution, and in addition a permanent moiety in chemical

combination with caloric.

Undisturbed by these conflicting views, that strangely original

genius, John Dalton, afterwards to be known as perhaps the greatest

of theoretical chemists, took the question in hand, and solved it by

showing that water exists in the air as an utterly independent gas. He

reached a partial insight into the matter in 1793, when his first volume

of meteorological essays was published; but the full elucidation of

the problem came to him in 1801. The merit of his studies was at once

recognized, but the tenability of his hypothesis was long and ardently

disputed.

While the nature of evaporation was in dispute, as a matter of course

the question of precipitation must be equally undetermined. The most

famous theory of the period was that formulated by Dr. Hutton in a paper

read before the Royal Society of Edinburgh, and published in the volume

of transactions which contained also the same author's epoch-making

paper on geology. This "theory of rain" explained precipitation as due

to the cooling of a current of saturated air by contact with a colder

current, the assumption being that the surplusage of moisture was

precipitated in a chemical sense, just as the excess of salt dissolved

in hot water is precipitated when the water cools. The idea that the

cooling of the saturated air causes the precipitation of its moisture

is the germ of truth that renders this paper of Hutton's important. All

correct later theories build on this foundation.

"Let us suppose the surface of this earth wholly covered with water,"

said Hutton, "and that the sun were stationary, being always vertical in

one place; then, from the laws of heat and rarefaction, there would be

formed a circulation in the atmosphere, flowing from the dark and cold

hemisphere to the heated and illuminated place, in all directions,

towards the place of the greatest cold.

"As there is for the atmosphere of this earth a constant cooling cause,

this fluid body could only arrive at a certain degree of heat; and this

would be regularly decreasing from the centre of illumination to the

opposite point of the globe, most distant from the light and heat.

Between these two regions of extreme heat and cold there would, in every

place, be found two streams of air following in opposite directions. If

those streams of air, therefore, shall be supposed as both sufficiently

saturated with humidity, then, as they are of different temperatures,

there would be formed a continual condensation of aqueous vapor, in some

middle region of the atmosphere, by the commixtion of part of those two

opposite streams.

"Hence there is reason to believe that in this supposed case there would

be formed upon the surface of the globe three different regions--the

torrid region, the temperate, and the frigid. These three regions would

continue stationary; and the operations of each would be continual. In

the torrid region, nothing but evaporation and heat would take place;

no cloud could be formed, because in changing the transparency of the

atmosphere to opacity it would be heated immediately by the operation of

light, and thus the condensed water would be again evaporated. But this

power of the sun would have a termination; and it is these that would

begin the region of temperate heat and of continual rain. It is not

probable that the region of temperance would reach far beyond the region

of light; and in the hemisphere of darkness there would be found a

region of extreme cold and perfect dryness.

"Let us now suppose the earth as turning on its axis in the equinoctial

situation. The torrid region would thus be changed into a zone, in

which there would be night and day; consequently, here would be much

temperance, compared with the torrid region now considered; and here

perhaps there would be formed periodical condensation and evaporation of

humidity, corresponding to the seasons of night and day. As temperance

would thus be introduced into the region of torrid extremity, so would

the effect of this change be felt over all the globe, every part of

which would now be illuminated, consequently heated in some degree. Thus

we would have a line of great heat and evaporation, graduating each way

into a point of great cold and congelation. Between these two extremes

of heat and cold there would be found in each hemisphere a region

of much temperance, in relation to heat, but of much humidity in the

atmosphere, perhaps of continual rain and condensation.

"The supposition now formed must appear extremely unfit for making this

globe a habitable world in every part; but having thus seen the effect

of night and day in temperating the effects of heat and cold in every

place, we are now prepared to contemplate the effects of supposing this

globe to revolve around the sun with a certain inclination of its axis.

By this beautiful contrivance, that comparatively uninhabited globe is

now divided into two hemispheres, each of which is thus provided with

a summer and a winter season. But our present view is limited to the

evaporation and condensation of humidity; and, in this contrivance of

the seasons, there must appear an ample provision for those alternate

operations in every part; for as the place of the vertical sun is moved

alternately from one tropic to the other, heat and cold, the original

causes of evaporation and condensation, must be carried over all the

globe, producing either annual seasons of rain or diurnal seasons of

condensation and evaporation, or both these seasons, more or less--that

is, in some degree.

"The original cause of motion in the atmosphere is the influence of the

sun heating the surface of the earth exposed to that luminary. We have

not supposed that surface to have been of one uniform shape and similar

substance; from whence it has followed that the annual propers of

the sun, perhaps also the diurnal propers, would produce a regular

condensation of rain in certain regions, and the evaporation of humidity

in others; and this would have a regular progress in certain determined

seasons, and would not vary. But nothing can be more distant from this

supposition, that is the natural constitution of the earth; for the

globe is composed of sea and land, in no regular shape or mixture, while

the surface of the land is also irregular with respect to its elevations

and depressions, and various with regard to the humidity and dryness of

that part which is exposed to heat as the cause of evaporation. Hence a

source of the most valuable motions in the fluid atmosphere with aqueous

vapor, more or less, so far as other natural operations will admit; and

hence a source of the most irregular commixture of the several parts of

this elastic fluid, whether saturated or not with aqueous vapor.

"According to the theory, nothing is required for the production of rain

besides the mixture of portions of the atmosphere with humidity, and of

mixing the parts that are in different degrees of heat. But we have seen

the causes of saturating every portion of the atmosphere with humidity

and of mixing the parts which are in different degrees of heat.

Consequently, over all the surface of the globe there should happen

occasionally rain and evaporation, more or less; and also, in every

place, those vicissitudes should be observed to take place with some

tendency to regularity, which, however, may be so disturbed as to be

hardly distinguishable upon many occasions. Variable winds and variable

rains should be found in proportion as each place is situated in an

irregular mixture of land and water; whereas regular winds should be

found in proportion to the uniformity of the surface; and regular rains

in proportion to the regular changes of those winds by which the mixture

of the atmosphere necessary to the rain may be produced. But as it will

be acknowledged that this is the case in almost all this earth where

rain appears according to the conditions here specified, the theory is

found to be thus in conformity with nature, and natural appearances are

thus explained by the theory."(1)

The next ambitious attempt to explain the phenomena of aqueous meteors

was made by Luke Howard, in his remarkable paper on clouds, published in

the Philosophical Magazine in 1803--the paper in which the names cirrus,

cumulus, stratus, etc., afterwards so universally adopted, were first

proposed. In this paper Howard acknowledges his indebtedness to Dalton

for the theory of evaporation; yet he still clings to the idea that

the vapor, though independent of the air, is combined with particles of

caloric. He holds that clouds are composed of vapor that has previously

risen from the earth, combating the opinions of those who believe

that they are formed by the union of hydrogen and oxygen existing

independently in the air; though he agrees with these theorists that

electricity has entered largely into the modus operandi of cloud

formation. He opposes the opinion of Deluc and De Saussure that clouds

are composed of particles of water in the form of hollow vesicles

(miniature balloons, in short, perhaps filled with hydrogen), which

untenable opinion was a revival of the theory as to the formation of all

vapor which Dr. Halley had advocated early in the eighteenth century.

Of particular interest are Howard's views as to the formation of dew,

which he explains as caused by the particles of caloric forsaking the

vapor to enter the cool body, leaving the water on the surface. This

comes as near the truth, perhaps, as could be expected while the old

idea as to the materiality of heat held sway. Howard believed, however,

that dew is usually formed in the air at some height, and that it

settles to the surface, opposing the opinion, which had gained vogue

in France and in America (where Noah Webster prominently advocated it),

that dew ascends from the earth.

The complete solution of the problem of dew formation--which really

involved also the entire question of precipitation of watery vapor in

any form--was made by Dr. W. C. Wells, a man of American birth, whose

life, however, after boyhood, was spent in Scotland (where as a young

man he enjoyed the friendship of David Hume) and in London. Inspired,

no doubt, by the researches of Mack, Hutton, and their confreres of

that Edinburgh school, Wells made observations on evaporation and

precipitation as early as 1784, but other things claimed his attention;

and though he asserts that the subject was often in his mind, he did not

take it up again in earnest until about 1812.

Meantime the observations on heat of Rumford and Davy and Leslie had

cleared the way for a proper interpretation of the facts--about the

facts themselves there had long been practical unanimity of opinion. Dr.

Black, with his latent-heat observations, had really given the clew to

all subsequent discussions of the subject of precipitation of vapor;

and from this time on it had been known that heat is taken up when water

evaporates, and given out again when it condenses. Dr. Darwin had shown

in 1788, in a paper before the Royal Society, that air gives off heat

on contracting and takes it up on expanding; and Dalton, in his essay

of 1793, had explained this phenomenon as due to the condensation and

vaporization of the water contained in the air.

But some curious and puzzling observations which Professor Patrick

Wilson, professor of astronomy in the University of Glasgow, had

communicated to the Royal Society of Edinburgh in 1784, and some similar

ones made by Mr. Six, of Canterbury, a few years later, had remained

unexplained. Both these gentlemen observed that the air is cooler where

dew is forming than the air a few feet higher, and they inferred

that the dew in forming had taken up heat, in apparent violation of

established physical principles.

It remained for Wells, in his memorable paper of 1816, to show that

these observers had simply placed the cart before the horse. He made it

clear that the air is not cooler because the dew is formed, but that

the dew is formed because the air is cooler--having become so through

radiation of heat from the solids on which the dew forms. The dew

itself, in forming, gives out its latent heat, and so tends to equalize

the temperature.

Wells's paper is so admirable an illustration of the lucid presentation

of clearly conceived experiments and logical conclusions that we should

do it injustice not to present it entire. The author's mention of

the observations of Six and Wilson gives added value to his own

presentation.

Dr. Wells's Essay on Dew