232 GEOLOGY. 



of the western half of the continent. To the life then on the globe 

 it must have been an event so appalling that the overthrow of 

 Pompeii and Herculaneum, and the great Lisbon earthquake, in 

 comparison with it, would have been an insignificant event. The 

 throes of this event must have shaken the globe and affected all 

 life, vegetable and animal. And as a matter of fact, the entire 

 facies of the animal life of the globe was changed from this time 

 forward, as we shall presently see. Thus was closed the Miocene 

 epoch. 



CHAPTER VI. 



TERTIARY PERIOD, CONTINUED.— PLIOCENE 



EPOCH. 



Inauguration of the Pliocene. — Extent of the Pliocene Lake of the Plains. — 

 Other Pliocene Lakes. — Eruptions at the beginning and during the Pliocene. 

 — Thickness of the Pliocene Beds. — Erosion of the Pliocene Beds. — Eleva- 

 tion of the Pliocene Deposits. — Eastward Barrier of the Pliocene Lake of 

 the Plains. — General Warren's Explanation. — Materials of the Pliocene 

 Beds. — Sections from the Niobrara, Loup and Driftwood. — General Character 

 in the Republican Valley. — So-called Tripoli Beds, and their Geyser Origin. 

 — Their Chemical Composition.— Nebraska Once a Geyser Region. — Length 

 of the Pliocene Epoch. — Vegetable Life. — Animal Life. — Rodents. — Horse 

 Eamily. — Camel Eamily. — Bisons. — Bear Family. — Cat Family. — Dog Family. 

 — Favorable Conditions during the Pliocene. — Picture of the Pliocene Epoch. 

 — Close of the Pliocene. — Convulsive Movements further West. — Gradual 

 Character of its Close. — General Remarks on the Tertiary Epochs. 



AT THE close of the last chapter it was stated how the Mio- 

 cene epoch came- to a close. At the opening of the Pliocene 

 epoch, the great Miocene lake of the plains underwent further sub- 

 sidence, but gently and gradually. There is no trace on the plains 

 of the intervention of a period of dry land, as some have supposed. 

 The Miocene lake here became the Pliocene by subsidence and 

 extension in every direction. It became much deeper than it had 

 been. " On the west it now reached the foot-hills of the Colorado 

 Range; on the south it enlarged the borders of the Miocene lake 

 from southern Nebraska, through Kansas, the Indian Territory, 

 far into Texas; on the north it stretched over the* whole- of the 



