THE TUNDRAS AND STEPPES OF PREHISTORIC! EUROPE. 339 



glaciers. Not only so, but by tracing the horizontal and vertical dis- 

 tribution of glacial phenomena we have been able to show what regions 

 were wholly ice covered, to measure the thickness attained by ice 

 sheets and glaciers, and to estimate the angle of their surface slope. 

 It is, in short, quite possible now to draw maps of Europe which shall 

 give a fairly accurate presentment of the aspect presented by our con- 

 tinent in glacial times. On maps of a sufficiently large scale we can 

 delineate not only the great inland ice of the north and northwest, but 

 the snow fields and numerous glaciers of the Alps and other moun- 

 tainous tracts, together with the areas covered by fluvio-glacial 

 deposits. 



So much for what we may call the physical evidence. But this is 

 not all, for associated with the true glacial accumulations occur in 

 many places beds charged with the remains of arctic-alpine plants and 

 animals. The evidence of fossil-organic remains, therefore, fully sup- 

 ports the conclusions arrived at from a study of purely glacial 

 phenomena. We know that arctic forms of life lived in our seas at 

 the time of which I am speaking, and that the countries outside of 

 the glaciated areas were then clothed and peopled by an arctic-alpine 

 flora and fauna. 



But, as if in contradiction of this evidence, certain other deposits 

 charged with the remains of temperate and southern species of plants 

 and animals appear intercalated among the true glacial accumulations. 

 The study of these and of their relation to subjacent and overlying 

 morainic and fluvio-glacial accumulations has led to the conclusion 

 that the Glacial period was not one continuous period of arctic condi- 

 tions, but a cycle or succession of alternating cold and genial epochs. 



So far as we at present know, glacial conditions first supervened in 

 late Tertiary times — in the so-called Pliocene period. In the earlier 

 part of that period the European climate had been singularly genial. 

 Warm seas, tenanted by many southern species of mollusks, washed 

 the shores of the British area, while the land was clothed with a much 

 more varied aud abundant flora than we now possess. Great forests 

 seem to have covered vast areas, occupying not only the plains and 

 the river valleys, but extending far up the mountain slopes of such 

 regions as France without much change of character. The same 

 species, indeed, appear to have flourished equally well in Cantal aud 

 central Italy. Some of these had come down from early Tertiary 

 times and were destined soon to become extinct; some, again, were 

 special forms belonging to genera which in our day are exotic; others 

 were species which have survived to the present in more southern and 

 eastern regions, while yet others are still represented in Europe by 

 identical or very closely allied species. Thus the flora of the Pliocene 

 was connected both with the past aud the present plant life of Europe, 

 while at the same time it had relations with the floras of distant 

 southern and eastern regions — with Florida, the Canary Islands, 



