GEOLOGICAL SURVEY OF THE TERRITORIES. 335 



made broad and all its topographical features softened down- In former 

 times, however, the topographical unity now conspicuous on the Plains 

 did not exist, and the surface was marked by a series of great basins 

 which received the flow of water from the Bocky Mountains and formed 

 lakes, less numerous, it is true, but of greater extent than those of the far 

 West. The northern portion of the eastern plateau has been Dr. Hayden's 

 chosen field of exploration for many years; a field he has well tilled, and 

 from which he has obtained a harvest of scientific truth which will form 

 for him an enduring and enviable monument. 



Among the most interesting researches of Dr. Hayden in this region 

 are the studies he has made of the deposits which have accumulated in 

 these great fresh-water basins. The story he has written of his explora- 

 tions of this district has been so well and fully told that I shall not 

 attempt to review it. Suffice it to say, that the series of fresh-water 

 basins discovered by Dr. Hayden in the country bordering the Upper 

 Missouri have proved to be as rich in new and interesting forms of animal 

 and vegetable life as any that have been found upon the earth's surface. 

 The vertebrate remains collected by Dr. Hayden have been carefully 

 studied, fully described and illustrated by Dr. Leidy, and the splendid 

 monograph which he has published of these fossils forms a contribu- 

 tion to paleontology not second in value or interest to that made by 

 Cuvier in his illustrations of the fossils from the Paris basin ; nor to 

 that of Falconer and Cautley, descriptive of the fossils of the Sewalik 

 Hills of India. 



The scarcely less voluminous and interesting collections of fossil 

 plants made by Dr. Hayden have been placed in my hands for examin- 

 ation. Of these, the first installments were described and drawn some 

 years since as a contribution to the report of Colonel W. F. Bayuolds, 

 United States Army, a report not yet published by the Government. 

 The descriptions, however, were printed in the annals of the Lyceum of 

 Natural History of New York, vol. 9, 1868. 



The general conclusions drawn from a study of this portion of Dr. 

 Hayden's collections as regards the floras of the tertiary and cretaceous 

 periods, the topography and climate of the interior of the continent — and 

 which form a part of my contribution to Colonel Eaynolds's report — will 

 be found quoted on another page. Since that report was written very 

 large additions have been made to our knowledge of our late extinct 

 floras, by collections of fossil plants made in different portions of the 

 western part of our continent by Dr. Hayden, Mr. Condon, Dr. Le Conte, 

 and myself; and also by the collections made by Mr. W. H. Dall and 

 Captaiu Howard in Alaska, and by several explorers on the continent 

 of Greenland. 



Deferring for the present a comparison of the plants derived from 

 strata of similar age in these widely separated localities, and the infer- 

 ences deducible from them as regards the physical geography of our 

 continent, I should say that the flora and fauna of the lake deposits on 

 both sides of the Eocky Mountains apparently belong to one and the 

 same geological age, and tell the same story in regard to the topography, 

 climate, conditions, and development of animal and vegetable life. There 

 is this striking difference, however, perceptible at the first glance be- 

 tween the fresh- water tertiaries of the East and West. In Oregon, Idaho, 

 and Nevada, volcanic materials have accumulated in the lake basins to 

 a much greater extent than east of the Eocky Mountains ; and we have 

 abundant evidence that during the tertiary period the western margin 

 of the continent was the scene of far greater volcanic activity than we 

 have any record of in the Eocky Mountain belt. 



