CHAPTER 18. — THE GLACIAL PERIOD IN NORTH AMERICA.
Post-glacial Strata containing Remains of Mastodon giganteus
in North America.
Scarcity of Marine Shells in Glacial Drift of Canada and the
United States.
Greater southern Extension of Ice-action in North America
than in Europe.
Trains of Erratic Blocks of vast Size in Berkshire, Massachusetts.
Description of their Linear Arrangement and Points of Departure.
Their Transportation referred to Floating and Coast Ice.
General Remarks on the Causes of former Changes of Climate at
successive geological Epochs.
Supposed Effects of the Diversion of the Gulf Stream in a
Northerly instead of North-Easterly Direction.
Development of extreme Cold on the opposite Sides of the Atlantic
in the Glacial period not strictly simultaneous.
Effect of Marine Currents on Climate.
Pleistocene Submergence of the Sahara.
On the North American continent, between the arctic circle and the 42nd parallel of latitude, we meet with signs of ice-action on a scale as grand as, if not grander than, in Europe; and there also the excess of cold appears to have been first felt at the close of the Tertiary, and to have continued throughout a large portion of the Pleistocene period. [Note 36]
The general absence of organic remains in the North American glacial formation makes it as difficult as in Europe to determine what mammalia lived on the continent at the time of the most intense refrigeration, or when extensive areas were becoming strewed over with glacial drift and erratic blocks, but it is certain that a large proboscidean now extinct, the Mastodon giganteus, Cuv., together with many other quadrupeds, some of them now living and others extinct, played a conspicuous part in the post-glacial era. By its frequency as a fossil species, this pachyderm represents the European Elephas primigenius, although the latter also occurs fossil in the United States and Canada, and abounds, as I learn from Sir John Richardson, in latitudes farther north than those to which the mastodon has been traced.
In the state of New York, the mastodon is not unfrequently met with in bogs and lacustrine deposits formed in hollows in the drift, and therefore, in a geological position, much resembling that of Recent peat and shell-marl in the British Isles, Denmark, or the valley of the Somme, as before described. Sometimes entire skeletons have been discovered within a few feet of the surface, in peaty earth at the bottom of small ponds, which the agriculturists had drained. The shells in these cases belong to freshwater genera, such as Limnaea, Physa, Planorbis, Cyclas, and others, differing from European species, but the same as those now proper to ponds and lakes in the same parts of America.
I have elsewhere given an account of several of these localities which I visited in 1842,* and can state that they certainly have a more modern aspect than almost all the European deposits in which remains of the mammoth occur, although a few instances are cited of Elephas Primigenius having been dug out of peat in Great Britain.
(* "Travels in North America" volume 1 page 55 London 1845;
and "Manual of Geology" chapter 12 5th edition page 144.)
Thus I was shown a mammoth's tooth in the museum at Torquay in Devonshire which is believed to have been dredged up from a deposit of vegetable matter now partially submerged beneath the sea. A more elevated part of the same peaty formation constitutes the bottom of the valley in which Tor Abbey stands. This individual elephant must certainly have been of more modern date than his fellows found fossil in the gravel of the Brixham cave, before described, for it flourished when the physical geography of Devonshire, unlike that of the cave period, was almost identical with that now established.
I cannot help suspecting that many tusks and teeth of the mammoth, said to have been found in peat, may be as spurious as are the horns of the rhinoceros cited more than once in the "Memoirs of the Wernerian Society" as having been obtained from shell-marl in Forfarshire and other Scotch counties; yet, between the period when the mammoth was most abundant and that when it died out, there must have elapsed a long interval of ages when it was growing more and more scarce; and we may expect to find occasional stragglers buried in deposits long subsequent in date to others, until at last we may succeed in tracing a passage from the Pleistocene to the Recent fauna, by geological monuments, which will fill up the gap before alluded to as separating the era of the flint tools of Amiens and Abbeville from that of the peat of the valley of the Somme.
How far the lacustrine strata of North America above mentioned may help to lessen this hiatus, and whether some individuals of the Mastodon giganteus may have come down to the confines of the historical period, is a question not so easily answered as might at first sight be supposed. A geologist might naturally imagine that the fluviatile formation of Goat Island, seen at the falls of Niagara, and at several points below the falls,* was very modern, seeing that the fossil shells contained in it are all of species now inhabiting the waters of the Niagara, and seeing also that the deposit is more modern than the glacial drift of the same locality.
(* "Travels in North America" by the author, volume 1
chapter 2 and volume 2 chapter 19.)
In fact, the old river bed, in which bones of the mastodon occur, holds the same position relatively to the boulder formation as the strata of shell-marl and bog-earth with bones of mastodon, so frequent in the State of New York, bear to the glacial drift, and all may be of contemporaneous date. But in the case of the valley of the Niagara we happen to have a measure of time which is wanting in the other localities, namely, the test afforded by the recession of the falls, an operation still in progress, by which the deep ravine of the Niagara, 7 miles long, between Queenstown and Goat Island has been hollowed out. This ravine is not only post-glacial, but also posterior in date to the fluviatile or mastodon-bearing beds. The individual therefore found fossil near Goat Island flourished before the gradual excavation of the deep and long chasm, and we must reckon its antiquity, not by thousands, but by tens of thousands of years, if I have correctly estimated the minimum of time which was required for the erosion of that great ravine.*
(* "Principles of Geology" 9th edition page 2; and "Travels
in North America" volume 1 page 32 1845.)
The stories widely circulated of bones of the mastodon having been observed with their surfaces pierced as if by arrow-heads or bearing the marks of wounds inflicted by some stone implement, must in future be more carefully inquired into, for we can scarcely doubt that the mastodon in North America lived down to a period when the mammoth co-existed with Man in Europe. But I need say no more on this subject, having already explained my views in regard to the evidence of the antiquity of Man in North America when treating of the human bone discovered at Natchez on the Mississippi.
In Canada and the United States we experience the same difficulty as in Europe when we attempt to distinguish between glacial formations of submarine and those of supra-marine origin. In the New World, as in Scotland and England, marine shells of this era have rarely been traced higher than 500 feet above the sea, and 700 feet seems to be the maximum to which at present they are known to ascend. In the same countries, erratic blocks have travelled from north to south, following the same direction as the glacial furrows and striae imprinted almost everywhere on the solid rocks underlying the drift. Their direction rarely deviates more than fifteen degrees east or west of the meridian, so that we can scarcely doubt, in spite of the general dearth of marine shells, that icebergs floating in the sea and often running aground on its rocky bottom were the instruments by which most of the blocks were conveyed to southern latitudes.
There are, nevertheless, in the United States, as in Europe, several groups of mountains which have acted as independent centres for the dispersion of erratics, as, for example, the White Mountains, latitude 44 degrees north, the highest of which, Mount Washington, rises to about 6300 feet above the sea; and according to Professor Hitchcock some of the loftiest of the hills of Massachusetts once sent down their glaciers into the surrounding lower country.
GREAT SOUTHERN EXTENSION OF TRAINS OF ERRATIC BLOCKS IN BERKSHIRE, MASSACHUSETTS, U.S., LATITUDE 42 DEGREES NORTH.
Having treated so fully in this volume of the events of the glacial period, I am unwilling to conclude without laying before the reader the evidence displayed in North America of ice-action in latitudes farther south by about ten degrees than any seen on an equal scale in Europe. This extension southwards of glacial phenomena in regions where there are no snow-covered mountains like the Alps to explain the exception, nor any hills of more than moderate elevation, constitutes a feature of the western as compared to the eastern side of the Atlantic, and must be taken into account when we speculate on the causes of the refrigeration of the northern hemisphere during the Pleistocene period.
(FIGURE 50. MAP SHOWING THE RELATIVE POSITION AND DIRECTION
OF SEVEN TRAINS OF ERRATIC BLOCKS IN BERKSHIRE, MASSACHUSETTS,
AND IN PART OF THE STATE OF NEW YORK.
Distance in a straight line, between the mountain ranges
A and C, about eight miles.
A. Canaan range, in the State of New York. The crest consists of
green chloritic rock.
B. Richmond range, the western division of which consists in
Merriman's Mount of the same green rock as A, but in a more
schistose form, while the eastern division is composed of
slaty limestone.
C. The Lenox range, consisting in part of mica-schist, and in some
districts of crystalline limestone.
d. Knob in the range A, from which most of the train Number 6 is
supposed to have been derived.
e. Supposed starting point of the train Number 5 in the range A.
f. Hiatus of 175 yards, or space without blocks.
g. Sherman's House.
h. Perry's Peak.
k. Flat Rock.
l. Merriman's Mount.
m. Dupey's Mount.
n. Largest block of train, Number 6. See Figures 51 and 52.
p. Point of divergence of part of the train Number 6, where a
branch is sent off to Number 5.
Number 1. The most southerly train examined by Messrs. Hall and
Lyell, between Stockbridge and Richmond, composed of blocks
of black slate, blue limestone and some of the green Canaan
rock, with here and there a boulder of white quartz.
Number 2. Train composed chiefly of large limestone masses, some
of them divided into two or more fragments by natural joints.
Number 3. Train composed of blocks of limestone and the green
Canaan rock; passes south of the Richmond Station on the Albany
and Boston railway; is less defined than Numbers 1 and 2.
Number 4. Train chiefly of limestone blocks, some of them thirty
feet in diameter, running to the north-west of the Richmond
Station, and passing south of the Methodist Meeting-house,
where it is intersected by a railway cutting.
Number 5. South train of Dr. Reid, composed entirely of large
blocks of the green chloritic Canaan rock; passes north of
the Old Richmond Meeting-house, and is three-quarters of a mile
north of the preceding train (Number 4).
Number 6. The great or principal train (north train of Dr. Reid),
composed of very large blocks of the Canaan rock, diverges at p,
and unites by a branch with train Number 5.
Number 7. A well-defined train of limestone blocks, with a few
of the Canaan rock, traced from the Richmond to the slope
of the Lenox range.)
In 1852, accompanied by Mr. James Hall, state geologist of New York, author of many able and well-known works on geology and palaeontology, I examined the glacial drift and erratics of the county of Berkshire, Massachusetts, and those of the adjoining parts of the state of New York, a district about 130 miles inland from the Atlantic coast and situated due west of Boston in latitude 42 degrees 25 minutes north. This latitude corresponds in Europe to that of the north of Portugal. Here numerous detached fragments of rock are seen, having a linear arrangement or being continuous in long parallel trains, running nearly in straight lines over hill and dale for distances of 5, 10, and 20 miles, and sometimes greater distances. Seven of the more conspicuous of these trains, from 1 to 7 inclusive, Figure 50, are laid down in the accompanying map or ground plan.*
(* This ground plan, and a farther account of the Berkshire
erratics was given in an abstract of a lecture delivered by
me to the Royal Institution of Great Britain, April 27, 1855
and published in their Proceedings.)
It will be remarked that they run in a north-west and south-east direction, or almost transversely to the ranges of hills A, B, and C, which run north-north-east and south-south-west. The crests of these chains are about 800 feet in height above the intervening valleys. The blocks of the northernmost train, Number 7, are of limestone derived from the calcareous chain B; those of the two trains next to the south, Numbers 6 and 5, are composed exclusively in the first part of their course of a green chloritic rock of great toughness, but after they have passed the ridge B, a mixture of calcareous blocks is observed. After traversing the valley for a distance of 6 miles these two trains pass through depressions or gaps in the range C, as they had previously done in crossing the range B, showing that the dispersion of the erratics bears some relation to the acutal inequalities of the surface, although the course of the same blocks is perfectly independent of the more leading features of the geography of the country, or those by which the present lines of drainage are determined. The greater number of the green chloritic fragments in trains 5 and 6 have evidently come from the ridge A, and a large proportion of the whole from its highest summit d, where the crest of the ridge has been worn into those dome-shaped masses called "roches moutonnees," already alluded to, and where several fragments having this shape, some of them 30 feet long, are seen in situ, others only slightly removed from their original position, as if they had been just ready to set out on their travels. Although smooth and rounded on their tops they are angular on their lower parts, where their outline has been derived from the natural joints of the rock. Had these blocks been conveyed from d by glaciers, they would have radiated in all directions from a centre, whereas not one even of the smaller ones is found to the westward of A, though a very slight force would have made them roll down to the base of that ridge, which is very steep on its western declivity. It is clear, therefore, that the propelling power, whatever it may have been, acted exclusively in a south-easterly direction. Professor Hall and I observed one of the green blocks—24 feet long, poised upon another about 19 feet in length. The largest of all on the west flank of m, or Dupey's Mount, called the Alderman, is above 90 feet in diameter, and nearly 300 feet in circumference. We counted at some points between forty and fifty blocks visible at once, the smallest of them larger than a camel.
(FIGURE 51. ERRATIC DOME-SHAPED BLOCK OF COMPACT CHLORITIC ROCK
(n in map in Figure 50), near the Richmond Meeting-house,
Berkshire, Massachusetts, latitude 42 degrees 25 minutes
North. Length, 52 feet; width, 40 feet; height above the
soil, 15 feet.)
The annexed drawing (Figure 51) represents one of the best known of train Number 6, being that marked n on the map (Figure 50). According to our measurement it is 52 feet long by 40 in width, its height above the drift in which it is partially buried being 15 feet. At the distance of several yards occurs a smaller block, 3 or 4 feet in height, 20 feet long, and 14 broad, composed of the same compact chloritic rock, and evidently a detached fragment from the bigger mass, to the lower and angular part of which it would fit on exactly. This erratic n has a regularly rounded top, worn and smoothed like the "roches moutonnees" before mentioned, but no part of the attrition can have occurred since it left its parent rock, the angles of the lower portion being quite sharp and unblunted.
(FIGURE 52. SECTION SHOWING THE POSITION OF THE BLOCK IN FIGURE 51.
a. The large block in Figure 51 and n in the map in Figure 50.
b. Fragment detached from the same.
c. Unstratified drift with boulders.
d. Silurian limestone in inclined stratification.)
From railway cuttings through the drift of the neighbourhood and other artificial excavations, we may infer that the position of the block n, if seen in a vertical section, would be as represented in Figure 52. The deposit c in that section consists of sand, mud, gravel, and stones, for the most part unstratified, resembling the till or boulder clay of Europe. It varies in thickness from 10 to 50 feet, being of greater depth in the valleys. The uppermost portion is occasionally, though rarely, stratified. Some few of the imbedded stones have flattened, polished, striated, and furrowed sides. They consist invariably, like the seven trains above mentioned, of kinds of rock confined to the region lying to the north-west, none of them having come from any other quarter. Whenever the surface of the underlying rock has been exposed by the removal of the superficial detritus, a polished and furrowed surface is seen, like that underneath a glacier, the direction of the furrows being from north-west to south-east, or corresponding to the course of the large erratics.
As all the blocks, instead of being dispersed from a centre, have been carried in one direction and across the ridges A, B, C and the intervening valleys, the hypothesis of glaciers is out of the question. I conceive, therefore, that the erratics were conveyed to the places they now occupy by coast ice, when the country was submerged beneath the waters of a sea cooled by icebergs coming annually from arctic regions.
(FIGURE 53. SECTION THROUGH CANAAN AND RICHMOND VALLEYS AT A TIME
WHEN THEY WERE MARINE CHANNELS.
d, e. Masses of floating ice carrying fragments of rock.)
Suppose the highest peaks of the ridges A, B, C in the annexed diagram (Figure 53) to be alone above water, forming islands, and d e to be masses of floating ice, which drifted across the Canaan and Richmond valleys at a time when they were marine channels, separating islands or rather chains of islands, having a north-north-east and south-south-west direction. A fragment of ice such as d, freighted with a block from A, might run aground and add to the heap of erratics at the north-west base of the island (now ridge) B, or, passing through a sound between B and the next island of the same group, might float on till it reached the channel between B and C. Year after year two such exposed cliffs in the Canaan range as d and e of the map, Figure 50, undermined by the waves, might serve as the points of departure of blocks, composing the trains Numbers 5 and 6. It may be objected that oceanic currents could not always have had the same direction; this may be true, but during a short season of the year when the ice was breaking up the prevailing current may have always run south-east.
If it be asked why the blocks of each train are not more scattered, especially when far from their source, it may be observed that after passing through sounds separating islands, they issued again from a new and narrow starting-point; moreover, we must not exaggerate the regularity of the trains, as their width is sometimes twice as great in one place in as another; and Number 6 sends off a branch at p, which joins Number 5. There are also stragglers, or large blocks here and there in the spaces between the two trains. As to the distance to which any given block would be carried, that must have depended on a variety of circumstances; such as the strength of the current, the direction of the wind, the weight of the block or the quantity and draught of the ice attached to it. The smaller fragments would, on the whole, have the best chance of going farthest; because, in the first place, they were more numerous, and then, being lighter, they required less ice to float them, and would not ground so readily on shoals, or if stranded, would be more easily started again on their travels. Many of the blocks, which at first sight seem to consist of single masses, are found when examined to be made up of two, three, or more pieces divided by natural joints. In the case of a second removal by ice, one or more portions would become detached and be drifted to different points further on. Whenever this happened, the original size would be lessened, and the angularity of the block previously worn by the breakers would be restored, and this tendency to split may explain why some of the far-transported fragments remain very angular.
These various considerations may also account for the fact that the average size of the blocks of all the seven trains laid down on the plan, Figure 50, lessens sensibly in proportion as we recede from the principal points of departure of particular kinds of erratics, yet not with any regularity, a huge block now and then recurring when the rest of the train consists of smaller ones.
All geologists acquainted with the district now under consideration are agreed that the mountain ranges A, B, and c, as well as the adjoining valleys, had assumed their actual form and position before the drift and erratics accumulated on and in them and before the surface of the fixed rocks was polished and furrowed. I have the less hesitation in ascribing the transporting power to coast-ice, because I saw in 1852 an angular block of sandstone, 8 feet in diameter, which had been brought down several miles by ice only three years before to the mouth of the Petitcodiac estuary, in Nova Scotia, where it joins the Bay of Fundy; and I ascertained that on the shores of the same bay, at the South Joggins, in the year 1850, much larger blocks had been removed by coast-ice, and after they had floated half a mile, had been dropped in salt water by the side of a pier built for loading vessels with coal, so that it was necessary at low tide to blast these huge ice-borne rocks with gunpowder in order that the vessels might be able to draw up alongside the pier. These recent exemplifications of the vast carrying powers of ice occurred in latitude 46 degrees north (corresponding to that of Bordeaux), in a bay never invaded by icebergs.
I may here remark that a sheet of ice of moderate thickness, if it extend over a wide area, may suffice to buoy up the largest erratics which fall upon it. The size of these will depend, not on the intensity of the cold but on the manner in which the rock is jointed, and the consequent dimensions of the blocks into which it splits when falling from an undermined cliff.
When I first endeavoured in the "Principles of Geology" in 1830,* to explain the causes, both of the warmer and colder climates which have at former periods prevailed on the globe, I referred to successive variations in the height and position of the land and its extent relatively to the sea in polar and equatorial latitudes—also to fluctuations in the course of oceanic currents and other geographical conditions, by the united influence of which I still believe the principal revolutions in the meteorological state of the atmosphere at different geological periods have been brought about.
(* 1st edition chapter 7; 9th edition ibid.)
The Gulf Stream was particularly alluded to by me as moderating the winter climate of northern Europe and as depending for its direction on temporary and accidental peculiarities in the shape of the land, especially that of the narrow Straits of Bahama, which a slight modification in the earth's crust would entirely alter.
Mr. Hopkins, in a valuable essay on the causes of former changes of climate,*nhas attempted to calculate how much the annual temperature of Europe would be lowered if this Gulf Stream were turned in some other and new direction, and estimates the amount at about six or seven degrees of Fahrenheit.
(* Hopkins, "Quarterly Journal of the Geological Society"
volume 8 1852 page 56.)
He also supposes that if at the same time a considerable part of northern and central Europe were submerged, so that a cold current from the arctic seas should sweep over it, an additional refrigeration of three or four degrees would be produced. He has speculated in the same essay on the effects which would be experienced in the eastern hemisphere if the same mighty current of warm water, instead of crossing the Atlantic, were made to run northwards from the Gulf of Mexico through the region now occupied by the valley of the Mississippi, and so onwards to the arctic regions.
After reflecting on what has been said in the thirteenth chapter of the submergence and re-elevation of the British Isles and the adjoining parts of Europe, and the rising and sinking of the Alps and the basins of some of the great rivers flowing from that chain, since the commencement of the glacial period, a geologist will not be disposed to object to the theory above adverted to, on the score of its demanding too much conversion of land into sea, or almost any amount of geographical change in Pleistocene times. But a difficulty of another kind presents itself. We have seen that, during the glacial period, the cold in Europe extended much farther south than it does at present, and in this chapter we have demonstrated that in North America the cold also extended no less than 10 degrees of latitude still farther southwards than in Europe; so that if a great body of heated water, instead of flowing north-eastward, were made to pass through what is now the centre of the American continent towards the Arctic Circle, it could not fail to mitigate the severity of the winter's cold in precisely those latitudes where the cold was greatest and where it has left monuments of ice-action surpassing in extent any exhibited on the European side of the ocean.
In the actual state of the globe, the isothermal lines, or lines of equal winter temperature when traced westward from Europe to North America bend 10 degrees south, there being a marked excess of winter cold in corresponding latitudes west of the Atlantic. During the glacial period, viewing it as a whole, we behold signs of a precisely similar deflection of these same isothermal lines when followed from east to west; so that if, in the hope of accounting for the former severity of glacial action in Europe, we suppose the absence of the Gulf Stream and imagine a current of equivalent magnitude to have flowed due north from the Gulf of Mexico, we introduce, as we have just hinted, a source of heat into precisely that part of the continent where the extreme conditions of refrigeration are most manifest. Viewed in this light, the hypothesis in question would render the glacial phenomena described in the present chapter more perplexing and anomalous than ever. But here another question arises, whether the eras at which the maximum of cold was attained on the opposite sides of the Atlantic were really contemporaneous? We have now discovered not only that the glacial period was of vast duration, but that it passed through various phases and oscillations of temperature; so that, although the chief polishing and furrowing of the rocks and transportation of erratics in Europe and North America may have taken place contemporaneously, according to the ordinary language of geology, or when the same testacea and the same Pleistocene assemblage of mammalia flourished, yet the extreme development of cold on the opposite sides of the ocean may not have been strictly simultaneous, but on the contrary the one may have preceded or followed the other by a thousand or more than a thousand centuries.
It is probable that the greatest refrigeration of Norway, Sweden, Scotland, Wales, the Vosges, and the Alps coincided very nearly in time; but when the Scandinavian and Scotch mountains were encrusted with a general covering of ice, similar to that now enveloping Greenland, this last country may not have been in nearly so glacial a condition as now, just as we find that the old icy crust and great glaciers, which have left their mark on the mountains of Norway and Sweden, have now disappeared, precisely at a time when the accumulation of ice in Greenland is so excessive. In other words, we see that in the present state of the northern hemisphere, at the distance of about 1500 miles, two meridional zones enjoying very different conditions of temperature may co-exist, and we are, therefore, at liberty to imagine some former alternations of colder and milder climates on the opposite sides of the ocean throughout the Pleistocene era of a compensating kind, the cold on the one side balancing the milder temperature on the other. By assuming such a succession of events we can more easily explain why there has not been a greater extermination of species, both terrestrial and aquatic, in polar and temperate regions during the glacial epoch, and why so many species are common to pre-glacial and post-glacial times.
The numerous plants which are common to the temperate zones north and south of the equator have been referred by Mr. Darwin and Dr. Hooker to migrations which took place along mountain chains running from north to south during some of the colder phases of the glacial epoch.*
(* Darwin, "Origin of Species" chapter 11 page 365; Hooker,
"Flora of Australia" Introduction page 18 1859.)
Such an hypothesis enables us to dispense with the doctrine that the same species ever originated independently in two distinct and distant areas; and it becomes more feasible if we admit the doctrine of the co-existence of meridional belts of warmer and colder climate, instead of the simultaneous prevalence of extreme cold both in the eastern and western hemisphere. It also seems necessary, as colder currents of water always flow to lower latitudes, while warmer ones are running towards polar regions, that some such compensation should take place, and that an increase of cold in one region must to a certain extent be balanced by a mitigation of temperature elsewhere.
Sir John F. Herschel, in his recent work on "Physical Geography," when speaking of the open sea which is caused in part of the polar regions by the escape of ice through Behring's Straits, and the flow of warmer water northwards through the same channel, observes that these straits, by which the continents of Asia and North America are now parted, "are only thirty miles broad where narrowest and only twenty-five fathoms in their greatest depth." But "this narrow channel," he adds, "is yet important in the economy of nature, inasmuch as it allows a portion of the circulating water from a warmer region to find its way into the polar basin, aiding thereby not only to mitigate the extreme rigour of the polar cold, but to prevent in all probability a continual accretion of ice, which else might rise to a mountainous height."*
(* Herschel's "Physical Geography" page 41 1861.)
Behring's Straits, here alluded to, happen to agree singularly in width and depth with the Straits of Dover, the difference in depth not being more than 3 or 4 feet; so that at the rate of upheaval, which is now going on in many parts of Scandinavia, of 2 1/2 feet in a century, such straits might be closed in 3000 years, and a vast accumulation of ice to the northward commence forthwith.
But, on the other hand, although such an accumulation might spread its refrigerating influence for many miles southwards beyond the new barrier, the warm current which now penetrates through the straits, and which at other times is chilled by floating ice issuing from them, would when totally excluded from all communication with the icy sea have its temperature raised and its course altered, so that the climate of some other area must immediately begin to improve.
There is still another probable cause of a vast change in the temperature of central Europe in comparatively modern times, to which no allusion has yet been made; namely, the conversion of the great desert of the Sahara from sea into land since the commencement of the Pleistocene period. When that vast region was still submerged, no sirocco blowing for days in succession carried its hot blasts from a wide expanse of burning sand across the Mediterranean. The south winds were comparatively cool, allowing the snows of the Alps to augment to an extent which the colossal dimensions of the moraines of extinct glaciers can alone enable us to estimate.
The scope and limits of this volume forbid my pursuing these speculations and reasonings farther; but I trust I have said enough to show that the monuments of the glacial period, when more thoroughly investigated, will do much towards expanding our views as to the antiquity of the fauna and flora now contemporary with Man, and will therefore enable us the better to determine the time at which Man began in the northern hemisphere to form part of the existing fauna. [Note 37]
CHAPTER 19. — RECAPITULATION OF GEOLOGICAL PROOFS OF MAN'S ANTIQUITY.
Recapitulation of Results arrived at in the earlier Chapters.
Ages of Stone and Bronze.
Danish Peat and Kitchen-Middens.
Swiss Lake-Dwellings.
Local Changes in Vegetation and in the wild and domesticated
Animals and in Physical Geography coeval with the Age of
Bronze and the later Stone Period.
Estimates of the positive Date of some Deposits of the later
Stone Period.
Ancient Division of the Age of Stone of St. Acheul and Aurignac.
Migrations of Man in that Period from the Continent to England
in Post-Glacial Times.
Slow Rate of Progress in barbarous Ages.
Doctrine of the superior Intelligence and Endowments of the
original Stock of Mankind considered.
Opinions of the Greeks and Romans, and their Coincidence with
those of the Modern Progressionist.
The ages of stone and bronze, so called by archaeologists, were spoken of in the earlier chapters of this work. That of bronze has been traced back to times anterior to the Roman occupation of Helvetia, Gaul, and other countries north of the Alps. When weapons of that mixed metal were in use, a somewhat uniform civilisation seems to have prevailed over a wide extent of central and northern Europe, and the long duration of such a state of things in Denmark and Switzerland is shown by the gradual improvement which took place in the useful and ornamental arts. Such progress is attested by the increasing variety of the forms, and the more perfect finish and tasteful decoration of the tools and utensils obtained from the more modern deposits of the bronze age, those from the upper layers of peat, for example, as compared to those found in the lower ones. The great number also of the Swiss lake-dwellings of the bronze age (about seventy villages having been already discovered), and the large population which some of them were capable of containing, afford indication of a considerable lapse of time, as does the thickness of the stratum of mud in which in some of the lakes the works of art are entombed. The unequal antiquity, also, of the settlements is occasionally attested by the different degrees of decay which the wooden stakes or piles have undergone, some of them projecting more above the mud than others, while all the piles of the antecedent age of stone have rotted away quite down to the level of the mud, such part of them only as was originally driven into the bed of the lake having escaped decomposition.*
(* Troyon, "Habitations lacustres" Lausanne 1860.)
Among the monuments of the stone period, which immediately preceded that of bronze, the polished hatchets called celts are abundant, and were in very general use in Europe before metallic tools were introduced. We learn, from the Danish peat and shell-mounds, and from the older Swiss lake-settlements, that the first inhabitants were hunters who fed almost entirely on game, but their food in after ages consisted more and more of tamed animals and still later a more complete change to a pastoral state took place, accompanied as population increased by the cultivation of some cereals.
Both the shells and quadrupeds belonging to the later stone period and to the age of bronze consist exclusively of species now living in Europe, the fauna being the same as that which flourished in Gaul at the time when it was conquered by Julius Caesar, even the Bos primigenius, the only animal of which the wild type is lost, being still represented, according to Cuvier, Bell, and Rutimeyer, by one of the domesticated races of cattle now in Europe.
These monuments, therefore, whether of stone or bronze, belong to what I have termed geologically the Recent period, the definition of which some may think rather too dependent on negative evidence, or on the non-discovery hitherto of extinct mammalia, such as the mammoth, which may one day turn up in a fossil state in some of the oldest peaty deposits, as indeed it is already said to have done at some spots, though I have failed as yet to obtain authentic evidence of the fact.*
(* A molar of E. primigenius, in a very fresh state, in the
museum at Torquay, believed to have been washed up by the
waves of the sea out of the submerged mass of vegetable
matter at the extremity of the valley in which Tor Abbey
stands, is the best case I have seen. See above, Chapter
18.)
No doubt some such exceptional cases may be met with in the course of future investigations, for we are still imperfectly acquainted with the entire fauna of the age of stone in Denmark as we may infer from an opinion expressed by Steenstrup, that some of the instruments exhumed by antiquaries from the Danish peat are made of the bones and horns of the elk and reindeer. Yet no skeleton or uncut bone of either of those species has hitherto been observed in the same peat.
Nevertheless, the examination made by naturalists of the various Danish and Swiss deposits of the Recent period has been so searching, that the finding in them of a stray elephant or rhinoceros, should it ever occur, would prove little more than that some few individuals lingered on, when the species was on the verge of extinction, and such rare exceptions would not render the classification above proposed inappropriate.
At the time when many wild quadrupeds and birds were growing scarce and some of them becoming locally extirpated in Denmark, great changes were taking place in the vegetation. The pine, or Scotch fir, buried in the oldest peat, gave place at length to the oak, and the oak, after flourishing for ages, yielded in its turn to the beech, the periods when these three forest trees predominated in succession tallying pretty nearly with the ages of stone, bronze, and iron in Denmark. In the same country also, during the stone period, various fluctuations, as we have seen, occurred in physical geography. Thus, on the ocean side of certain islands, the old refuse-heaps, or "kitchen-middens," were destroyed by the waves, the cliffs having wasted away, while on the side of the Baltic, where the sea was making no encroachment or where the land was sometimes gaining on the sea, such mounds remained uninjured. It was also shown that the oyster, which supplied food to the primitive people, attained its full size in parts of the Baltic where it cannot now exist owing to a want of saltness in the water, and that certain marine univalves and bivalves, such as the common periwinkle, mussel, and cockle, of which the castaway shells are found in the mounds, attained in the olden time their full dimensions, like the oysters, whereas the same species, though they still live on the coast of the inland sea adjoining the mounds, are dwarfed and never half their natural size, the water being rendered too fresh for them by the influx of so many rivers.
Some archaeologists and geologists of merit have endeavoured to arrive at positive dates, or an exact estimate of the minimum of time assignable to the later age of stone. These computations have been sometimes founded on changes in the level of the land, or on the increase of peat, as in the Danish bogs, or on the conversion of water into land by alluvial deposits, since certain lake-settlements in Switzerland were abandoned. Alterations also in the geographical distribution or preponderance of certain living species of animals and plants have been taken into account in corroboration, as have the signs of progress in human civilisation, as serving to mark the lapse of time during the stone and bronze epochs.
M. Morlot has estimated with care the probable antiquity of three superimposed vegetable soils cut open at different depths in the delta of the Tiniere, each containing human bones or works of art, belonging successively to the Roman, bronze, and later stone periods. According to his estimate, an antiquity of 7000 years at least must be assigned to the oldest of these remains, though believed to be long posterior in date to the time when the mammoth and other extinct mammalia flourished together with Man in Europe. Such computations of past time must be regarded as tentative in the present state of our knowledge and much collateral evidence will be required to confirm them; yet the results appear to me already to afford a rough approximation to the truth.
Between the newer or Recent division of the stone period and the older division, which has been called the Pleistocene, there was evidently a vast interval of time—a gap in the history of the past, into which many monuments of intermediate date will one day have to be intercalated. Of this kind are those caves in the south of France, in which M. Lartet has lately found bones of the reindeer, associated with works of art somewhat more advanced in style than those of St. Acheul or of Aurignac. In the valley of the Somme we have seen that peat exists of great thickness, containing in its upper layers Roman and Celtic memorials, the whole of which has been of slow growth, in basins or depressions conforming to the present contour and drainage levels of the country, and long posterior in date to older gravels, containing bones of the mammoth and a large number of flint implements of a very rude and antique type. Some of those gravels were accumulated in the channels of rivers which flowed at higher levels by 100 feet than the present streams, and before the valley had attained its present depth and form. No intermixture has been observed in those ancient river beds of any of the polished weapons, called "celts," or other relics of the more modern times, or of the second or Recent stone period, nor any interstratified peat; and the climate of those Pleistocene ages, when Man was a denizen of the north-west of France and of southern and central England, appears to have been much more severe in winter than it is now in the same region, though far less cold than in the glacial period which immediately preceded.
We may presume that the time demanded for the gradual dying out or extirpation of a large number of wild beasts which figure in the Pleistocene strata and are missing in the Recent fauna was of protracted duration, for we know how tedious a task it is in our own times, even with the aid of fire-arms, to exterminate a noxious quadruped, a wolf, for example, in any region comprising within it an extensive forest or a mountain chain. In many villages in the north of Bengal, the tiger still occasionally carries off its human victims, and the abandonment of late years by the natives of a part of the Sunderbunds or lower delta of the Ganges, which they once peopled, is attributed chiefly to the ravages of the tiger. It is probable that causes more general and powerful than the agency of Man, alterations in climate, variations in the range of many species of animals, vertebrate and invertebrate, and of plants, geographical changes in the height, depth, and extent of land and sea, some or all of these combined, have given rise in a vast series of years to the annihilation, not only of many large mammalia, but to the disappearance of the Cyrena fluminalis, once common in the rivers of Europe, and to the different range or relative abundance of other shells which we find in the European drifts.
That the growing power of Man may have lent its aid as the destroying cause of many Pleistocene species, must, however, be granted; yet, before the introduction of fire-arms, or even the use of improved weapons of stone, it seems more wonderful that the aborigines were able to hold their own against the cave-lion, hyaena, and wild bull, and to cope with such enemies, than that they failed to bring about their speedy extinction.
It is already clear that Man was contemporary in Europe with two species of elephant, now extinct, E. primigenius and E. antiquus, two also of rhinoceros, R. tichorhinus and R. hemitoechus (Falc.), at least one species of hippopotamus, the cave-bear, cave-lion, and cave-hyaena, various bovine, equine, and cervine animals now extinct, and many smaller Carnivora, Rodentia, and Insectivora. While these were slowly passing away, the musk ox, reindeer, and other arctic species which have survived to our times were retreating northwards from the valleys of the Thames and Seine to their present more arctic haunts.
The human skeletons of the Belgian caverns of times coeval with the mammoth and other extinct mammalia do not betray any signs of a marked departure in their structure, whether of skull or limb, from the modern standard of certain living races of the human family. As to the remarkable Neanderthal skeleton (Chapter 5), it is at present too isolated and exceptional, and its age too uncertain, to warrant us in relying on its abnormal and ape-like characters, as bearing on the question whether the farther back we trace Man into the past, the more we shall find him approach in bodily conformation to those species of the anthropoid quadrumana which are most akin to him in structure.
In the descriptions already given of the geographical changes which the British Isles have undergone since the commencement of the glacial period (as illustrated by several maps, Figures 39 to 41), it has been shown that there must have been a free communication by land between the Continent and these islands, and between the several islands themselves, within the Pleistocene epoch, in order to account for the Germanic fauna and flora having migrated into every part of the area, as well as for the Scandinavian plants and animals to have retreated into the higher mountains. During some part of the Pleistocene ages, the large pachyderms and accompanying beasts of prey, now extinct, wandered from the Continent to England; and it is highly probable that France was united with some part of the British Isles as late as the period of the gravels of St. Acheul and the era of those engulfed rivers which, in the basin of the Meuse near Liege, swept into many a rent and cavern the bones of Man and of the mammoth and cave-bear. There have been vast geographical revolutions in the times alluded to, and oscillations of land, during which the English Channel, which can be shown by the Pagham erratics and the old Brighton beach (Chapter 14), to be of very ancient origin, may have been more than once laid dry and again submerged. During some one of these phases, Man may have crossed over, whether by land or in canoes, or even on the ice of a frozen sea (as Mr. Prestwich has hinted), for the winters of the period of the higher-level gravels of the valley of the Somme were intensely cold.
The primitive people, who co-existed with the elephant and rhinoceros in the valley of the Ouse at Bedford, and who made use of flint tools of the Amiens type, certainly inhabited part of England which had already emerged from the waters of the glacial sea and the fabricators of the flint tools of Hoxne, in Suffolk, were also, as we have seen, post-glacial. We may likewise presume that the people of Pleistocene date, who have left their memorials in the valley of the Thames, were of corresponding antiquity, posterior to the boulder clay but anterior to the time when the rivers of that region had settled into their present channels.
The vast distance of time which separated the origin of the higher and lower gravels of the valley of the Somme, both of them rich in flint implements of similar shape (although those of oval form predominate in the newer gravels), leads to the conclusion that the state of the arts in those early times remained stationary for almost indefinite periods. There may, however, have been different degrees of civilisation and in the art of fabricating flint tools, of which we cannot easily detect the signs in the first age of stone, and some contemporary tribes may have been considerably in advance of others. Those hunters, for example, who feasted on the rhinoceros and buried their dead with funeral rites at Aurignac may have been less barbarous than the savages of St. Acheul, as some of their weapons and utensils have been thought to imply. To a European who looks down from a great eminence on the products of the humble arts of the aborigines of all times and countries, the stone knives and arrows of the Red Indian of North America, the hatchets of the native Australian, the tools found in the ancient Swiss lake-dwellings or those of the Danish kitchen-middens and of St. Acheul, seem nearly all alike in rudeness and very uniform in general character. The slowness of the progress of the arts of savage life is manifested by the fact that the earlier instruments of bronze were modelled on the exact plan of the stone tools of the preceding age, although such shapes would never have been chosen had metals been known from the first. The reluctance or incapacity of savage tribes to adopt new inventions has been shown in the East by their continuing to this day to use the same stone implements as their ancestors, after that mighty empires, where the use of metals in the arts was well known, had flourished for three thousand years in their neighbourhood.
We see in our own times that the rate of progress in the arts and sciences proceeds in a geometrical ratio as knowledge increases, and so when we carry back our retrospect into the past, we must be prepared to find the signs of retardation augmenting in a like geometrical ratio; so that the progress of a thousand years at a remote period may correspond to that of a century in modern times, and in ages still more remote Man would more and more resemble the brutes in that attribute which causes one generation exactly to imitate in all its ways the generation which preceded it.
The extent to which even a considerably advanced state of civilisation may become fixed and stereotyped for ages, is the wonder of Europeans who travel in the East. One of my friends declared to me, that whenever the natives expressed to him a wish "that he might live a thousand years," the idea struck him as by no means extravagant, seeing that if he were doomed to sojourn for ever among them, he could only hope to exchange in ten centuries as many ideas, and to witness as much progress as he could do at home in half a century.
It has sometimes happened that one nation has been conquered by another less civilised though more warlike, or that during social and political revolutions, people have retrograded in knowledge. In such cases, the traditions of earlier ages, or of some higher and more educated caste which has been destroyed, may give rise to the notion of degeneracy from a primaeval state of superior intelligence, or of science supernaturally communicated. But had the original stock of mankind been really endowed with such superior intellectual powers and with inspired knowledge and had possessed the same improvable nature as their posterity, the point of advancement which they would have reached ere this would have been immeasurably higher. We cannot ascertain at present the limits, whether of the beginning or the end, of the first stone period when Man co-existed with the extinct mammalia, but that it was of great duration we cannot doubt. During those ages there would have been time for progress of which we can scarcely form a conception, and very different would have been the character of the works of art which we should now be endeavouring to interpret—those relics which we are now disinterring from the old gravel-pits of St. Acheul, or from the Liege caves. In them, or in the upraised bed of the Mediterranean, on the south coast of Sardinia, instead of the rudest pottery or flint tools so irregular in form as to cause the unpractised eye to doubt whether they afford unmistakable evidence of design, we should now be finding sculptured forms surpassing in beauty the masterpieces of Phidias or Praxiteles; lines of buried railways or electric telegraphs from which the best engineers of our day might gain invaluable hints; astronomical instruments and microscopes of more advanced construction than any known in Europe, and other indications of perfection in the arts and sciences such as the nineteenth century has not yet witnessed. Still farther would the triumphs of inventive genius be found to have been carried, when the later deposits, now assigned to the ages of bronze and iron, were formed. Vainly should we be straining our imaginations to guess the possible uses and meaning of such relics—machines, perhaps, for navigating the air or exploring the depths of the ocean, or for calculating arithmetical problems beyond the wants or even the conception of living mathematicians.
The opinion entertained generally by the classical writers of Greece and Rome, that Man in the first stage of his existence was but just removed from the brutes, is faithfully expressed by Horace in his celebrated lines, which begin:—
Quum prorepserunt primis animalia terris.—Sat. lib. 1, 3, 99.
The picture of transmutation given in these verses, however severe and contemptuous the strictures lavishly bestowed on it by Christian commentators, accords singularly with the train of thought which the modern doctrine of progressive development has encouraged.
"When animals," he says, "first crept forth from the newly formed earth, a dumb and filthy herd, they fought for acorns and lurking-places with their nails and fists, then with clubs, and at last with arms, which, taught by experience, they had forged. They then invented names for things and words to express their thoughts, after which they began to desist from war, to fortify cities and enact laws." They who in later times have embraced a similar theory, have been led to it by no deference to the opinions of their pagan predecessors, but rather in spite of very strong prepossessions in favour of an opposite hypothesis, namely, that of the superiority of their original progenitors, of whom they believe themselves to be the corrupt and degenerate descendants.
So far as they are guided by palaeontology, they arrive at this result by an independent course of reasoning; but they have been conducted partly to the same goal as the ancients by ethnological considerations common to both, or by reflecting in what darkness the infancy of every nation is enveloped and that true history and chronology are the creation, as it were, of yesterday.