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v 
superior races by conquest or commerce, bythe evolution of native 
populations from the rude conditions of the neolithic period. Nor 
does this neolithic period afford us much assistance. It is of 
extreme interest as showing the progress of civilization in pre- 
historic times among the early races of Europe, and enabling 
us to trace the origin of many of its existing populations. But 
for chronological purposes we are met by the difficulty that the 
historical records of Egypt and Chaldea go back so far that we 
can find no assurance that even the earlier of the Swiss Lake 
dwellings, may not have been contemporary with, or subsequent 
to, the great dynasties of Memphis and of Babylon. In those 
countries whose history goes so far back, the neolithic period is 
buried under the ruins of civilization, and the accumulations of 
alluvial deposits, and the traces which connect the dyke of Menes 
and the Pyramids with the preceding stone age, are few and far 
between. All we know for certain in Egypt is that borings in 
the Nile Valley have brought up fragments of pottery, apparently 
of neolithic age, from depths which are conjectured to show an 
accumulation of Nile deposits at the existing rate for about 18,000 
years back, that neolithic flint implements have been found at 
various points near Cairo and Thebes, and that celts and scrapers 
of the usual paleolithic type have been found in gravels of un- 
doubted quaternary antiquity in ravines near Thebes. In 
Chaldea the connections of the ancient civilization with a stone 
age is even slighter, and reduces itself to the fact that palzolithic 
implements have been found near Bagdad in old gravels of the 
Euphrates and Tigris. When we wish, therefore, to retrace the 
stream of human origin beyond the period of perhaps 10,000 
years, which is the shortest time we can allow for the growth of 
such a civilization as we find actually existing 7,000 years ago, we 
have to fall back exclusively on considerations drawn from the 
exact sciences, such as geology, astronomy, anthropology, and 
paleontology. The key of the problem is in the glacial period. 
THe GLACIAL PERIOD. 
It is clearly established that the recent period during which the 
conditions of climate, physical geography, fauna and flora, have 
been substantially the same as at present, was preceded by a 
long glacial period, during portions of which a great part of 
Europe and America were buried under ice-caps and glaciers. It 
is clear also that this glacial period did not consist of one appear- 
ance and disappearance of intense cold, in comparatively recent 
times, but that it came on towards the end of the pliocene age ; 
rose rapidly to a maximum of intensity when an ice-cap from 
Scandinavia filled the Northern Seas, overflowed mountain chains, 
and carried its boulders as far south as the Thames Valley and 
central Germany ; while gigantic glaciers from the Alps and other 
chains of lofty mountains buried Switzerland, choked up the 
