THE TERTIARY PERIOD. 2-19 



cene America, herbivorous life was so dominant that it could suc- 

 cessfully defend itself against the carnivora, and the latter evidently 

 obtained most of their prey by stealth and by picking off the aged 

 and infirm. Animal life is generally happy when it is left alone, 

 and this was specially the case during American Pliocene times. 

 It is a grave reflection on humanity that, not the Creator, but man's 

 injustice and inhumanity, produces most of the misery which we see 

 in the world. This is, however, but a very faint picture of these 

 happy Pliocene times which lasted for untold ages. But every one 

 can, for himself, by "the aid of the scientific imagination," form 

 such pictures of the wonders of that old-time world. 



Close of the Pliocene Epoch. — There is evidence that the Pliocene 

 epoch only gradually came to a close. The lake of the plains was 

 probably partially drained, and a large part of its surface became 

 dry land long before the last centuries of the Pliocene had ended. 

 Clarence King describes a series " of coarse semi-stratified gravels 

 and conglomerates" along the eastern base of the Colorado Range, 

 which, "in the benches of the Sybille, distinctly overlie the Nio- 

 brara Pliocene, which abut against the Archaean core of the range," 

 from which these materials were derived. The same formations 

 are found at the head of the Chugwater, the valley of the Big 

 Thompson, and at other points. In places on these streams, these 

 gravels are from 200 to 300 feet thick, and descend in rude terraces. 

 As these formations, according to King, overlie the Niobrara Plio- 

 cene, and antedate the Quarternary, they evidently constitute the 

 closing deposits of the Pliocene epoch. I have detected the equiv- 

 alents of these deposits nowhere in Nebraska, even where it is least 

 eroded. It is probable, therefore, that the great lake of the plains 

 was drained before these deposits were laid down. The eastern 

 border of the great Pliocene rim commenced to descend and gradu- 

 ally left out the water until much of this great lake of the plains 

 became dry land. There is also evidence of increasing cold in the 

 deposits of this lake through their upper sections. The southern 

 shores of the lake were probably rising -t the same time, which 

 would help to intensify the growing cold. An ice cap had now 

 formed in polar regions, and conditions of climate similar to the 

 present intervened. Age after age the increasing cold, accompanied 

 by gradual elevation of land towards the north, continued, until 

 finally the Arctic ice cap crept down to our present temperate lati- 

 tudes. The flora and fauna of the Pliocene migrated southward, 



