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366

MERIDIONAL ZONES

CHAP. XVIII.

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 post-pliocene 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 fifteen hundred 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 post-pliocene 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

CHAP. XVIII.

OF COLDER AND MILDER CLIMATE.

367

zones N. and S. of the equator have been referred by Mr. Darwin and Dr. Hooker to migrations, which took place along mountain chains running from N. to S. during some of the colder phases of the glacial epoch.* 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.

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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.' †

Behring's Straits, here alluded to, happen to agree singularly in width and depth with the Straits of Dover, the difference

* Darwin, Origin of Species, ch. xi. p. 365; Hooker, Flora of Australia, Introduction, p. xviii.

† Herschel's Physical Geography, p. 41, 1861.

368

CLIMATE AFFECTED BY CURRENTS.

CHAP. XVIII.

in depth not being more than three or four feet; so that at the rate of upheaval, which is now going on in many parts of Scandinavia, of two and a half 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.

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.

CHAP. XIX.

RECAPITULATION OF RESULTS.

369

CHAPTER XIX.

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 PERIODANCIENT 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 IN-
TELLIGENCE AND ENDOWMENTS OF THE ORIGINAL STOCK OF MANKIND
CONSIDERED OPINIONS OF THE GREEKS AND ROMANS, AND THEIR
COINCIDENCE WITH THOSE OF THE MODERN PROGRESSIONIST EARLY
EGYPTIAN CIVILISATION AND ITS DATE IN COMPARISON WITH THAT OF
THE FIRST AND SECOND STONE PERIODS.

HE ages of stone and bronze, so called by archæologists,

THE

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

B B

370

RECAPITULATION OF RESULTS.

CHAP. XIX.

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.*

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 (p. 21).

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 Cæsar, even the Bos primigenius, the only animal of which the wild type is lost, being still represented, according to Cuvier, Bell, and Rütimeyer, by one of the domesticated races of cattle now in Europe. (See p. 25.)

Troyon, Habitations lacustres. Lausanne, 1860.

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