124 SKETCH OF THE HISTORY OF MAMMALIA. 



tween the tribes of the Atlantic and the Pacific oceans 

 of our day. The general features of land and sea as 

 they now exist began to appear, and there can be no 

 doubt that in a philosophical study of the revolutions of 

 the globe the tertiary era of geology cannot be properly 

 separated from the existing system of nature," The 

 tertiary period, taken in this extended sense, saw the 

 creation and extinction of the mammoth, the mastodon, 

 the palseotherium, the fossil rhinoceros and hippopotamus, 

 the dinotherium, the toxodon, and the huge pachyderm 

 of Australia ; and next, the creation of all our modern 

 races of animals. 



During the period of the deposition of the tertiary 

 strata, the relations of land and sea were greatly altered 

 in various portions of the globe ; in Europe by the rising 

 of the Pyrenees beyond the height they reached after 

 the cretaceous era, and by the uplifting of the Alps from 

 the Mediterranean towards Mont Blanc. " In England 

 we may believe the upward movement of the southern 

 counties connected with the Hampshire axis of elevation 

 and the Isle of Wight convulsion was ended at an early 

 epoch of the tertiary period. The eastern range of the 

 Alps from Mont Blanc to Vienna is of later date, and 

 may be viewed as the most marked phenomenon of ele- 

 vation which accompanied or preceded the dispersion of 

 erratic blocks in Europe." 



Besides the alterations thus produced in the relation 

 of the land and the sea, changes have taken place, and 

 are still in progress, from other causes. Rivers bring 

 down vast quantities of the disintegrated particles of the 

 strata through which they flow, and deposit the sediment 

 at their mouths, forming deltas, or low tracts, won as it 

 were particle by particle from the domain of the ocean ; 

 on the other hand, the sea itself wears down coasts to a 

 great extent, making vast inroads on the land, and con- 

 verting the isthmus into an island: sometimes, by the 

 sudden or gradual elevation of a large tract of land, an 

 inland sea becomes drained, leaving in its place a sandy 

 desert. In the depths themselves there is no rest ; 

 multitudes of zoophytes and testacea there live and die. 



