226 THE BOUNDARY-LINE BETWEEN GEOLOGY AND HISTORY. 



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 pens that a large portion of Central Europe is to-day covered with a 

 bowlder formation of Scandinavian or Finnic origin. 



2. The following epoch is, on the contrary, one of extensive and con- 

 siderable upheaval or elevation, whicli has been specially studied by the 

 English geologist Austin. While the sea had before extended so far 

 into Central Europe, all the sea-bottom between Ireland, France, En- 

 gland, and Scandinavia was now raised above the surface of the water, 

 and our continent extended as far as the Shetland Islands. What is 

 to-day the North Sea was then an extensive lowland, traversed, no doubt, 

 by a large stream, the continuation of the present Rhine, which then 

 had the Elbe and the Thames for tributaries, and its mouth far to the 

 northward. Even at the present day fishers find in the deeper portions 

 of the ISTorth Sea bones of deer and elephants, which once lived on the 

 banks of that great river. On many i^ortions of its banks submerged 

 forests are known to exist, reaching far below the present sea. The 

 present bottom of the sea presents a line of steep descent at a depth of 

 about 200 fathoms. This line runs west of Scotland and of Ireland, in- 

 cluding, therefore, that island also, and approaches the i^reseut continent 

 only in the direction of the Bay of Biscay. There is some reason for 

 supposing that this line indicates the former outlines of Europe. 



3. The next epoch was that of the depression, which gave the conti- 

 nent of Europe its present form. 



The most important changes which can be recognized in Europe at 

 so late a period are a severer climate and repeated alterations in the dis- 

 tribution of water and land. Astonishing as these phenomena may 

 appear, a glance at the present state of things will demonstrate their 

 possibility. 



Europe possesses at present an exceptionally mild climate; a stream 

 of warm water coming from the Gulf of Mexico washes and warms the 

 greater part of its western coast ; warm currents of air blow over its 

 southern parts from the Desert of Sahara, and the absence of a large ex- 

 tent of country near the north i^ole prevents the accumulation of great 

 masses of snow, and the cold winds resulting from it. But all these 

 favorable conditions could be completely removed by a change in the 

 distribution of land and water. Such changes are, indeed, still going 

 on in some places. A portion of Sweden is known to be rising, while 

 a part of Greenland is sinking with considerable rapidity. 



Having thus far considered only the inorganic world, let us now turn our 

 attention to the organized beings which inhabit Central Europe under 

 the above circumstances, and we will see that their character entirely 

 corresponds to a severer climate. 



The remains of the land-animals of those times are found either in 

 alluvium or in caves. An alluvium of yellowish-brown clay, found in 

 most river-valleys of Central Europe, is formed by fresh-water rivers 

 or lakes, and contains no sea-shells. In it we find the shells of various 

 land-snails and the remains of herbivorous mammals much more fre- 



