212 GEOLOGY. 



of an inch of solid sediment, on an average, could accumulate in a 

 year. It was probably far less rapid than that, but even at that 

 rate, over half a million of years were required to accumulate these 

 12,000 feet of sediments that are left from these old lake beds. 

 During the progress of these deposits, there were occasional oscil- 

 lations of level and interruptions in the accumulation of materials. 

 This is indicated by the shifting of the shore lines westward, and 

 the slight unconformability of the Green River beds with the under- 

 lying Vermillion. 



We can best understand the progressive movements, and the ad- 

 vanced position of those times by considering the vegetable and 

 animal life which is found entombed in its various groups. 



It was the great changes in climate resulting from the changes 

 in physical geography, that either exterminated the vegetable and 

 animal life of the preceding Cretaceous period, or by gradual change 

 of environment transforming them into the advanced stages which 

 they exhibited during the opening centuries of the Eocene. 



Life during the Vermillion Creek Period. Wasatch of Hayden. — In 

 the sediments of this group (5 ,000 feet thick), have been found, and 

 described by Lesquereux, forty-six species of plants. Among these 

 are found the following notable forms: One Cypress (Taxodium 

 dubium), one Giant Cedar {Sequoia Heerii), one Sweet Gum Tree 

 {Liquidamber gracilis), six species of Cottonwood {Populus), one 

 Alder {Alnus Kefersleinii), one Birch (Betula Slevensoni), five Oaks 

 (Querais), two Hazel-nuts (Corylus), two Beeches {Fagus), five figs 

 (Ficus), two Sycamores (Platanus), two Dogwoods (Cornus), one 

 Magnolia, one Papaw {Asimina mioceneca), one Grape-vine, three 

 Walnuts (Juglans), and twenty-one other species. These vegetable 

 forms, according to Lesquereux, are, when compared with Euro- 

 pean fossils, all of Miocene type, though found here in the lower 

 Eocene. In fact, of the fifty-six species, thirty-one are identical 

 with the European Miocene, or the Arctic Miocene Flora. Accord- 

 ing to the same authority, they are indicative of a warm temperate 

 climate. This is specially indicated by the presence of the Magno- 

 lia, Fig Trees, Sequoias and Cypress. 



Animal Life of the Ver?nillio?i Group Epoch. — The peculiarity 

 that marked the animal life of the earliest Eocene was the sudden 

 appearance of mammals of a high type. Though highly generalized 

 compared with their more modern representatives, the transition 

 forms connecting them with the animals of the preceding Cretace- 



