No. 5.] NATURAL HISTORY SOCIETY. 28& 



history of these great prairie lands is thus as plain and simple 

 as their own superficial features. First, we have a great Cre- 

 taceous 3IediterraneaD, extending from the Gulf of Mexico per- 

 haps to the Arctic sea. Then we have this dried up into estu- 

 aries, lakes and marshes, and becoming clothed with a rich vege- 

 tation similar in general character to that of the west coast at 

 present, and indicating a mild and genial climate. Then we 

 have the great Post-pliocene subsidence, with its trains of gravel 

 and ice-borne boulders ; and lastly the re-elevation into the 

 prairie lands of to-day, with perhaps an intervening age of 

 modern forests- The final results are a vast expanse of fertile 

 soil, and great stores of mineral fuel, which may one day make 

 these now lone lands the seats of extensive manufacturing indus- 

 trie"--. Detailed reports of the explorations of the past year are 

 in progress, and will greatly increase our precise and definite 

 knowledge of regions which have hitherto been known to us 

 principally through the vague impressions of unscientific travel- 

 lers. 



Simple though the structure of these Western regions is, it 

 has already given rise to controversies, more especially with 

 reference to the age of the plants and animals whose remains 

 have been fcund in these formations south of the United States 

 houndary. In looking over these controversies, I am inclined in 

 the first place to believe that we have in the West a gradual 

 passage from the Cretaceous to the Tertiary beds, and that these 

 last may scarcely admit of a definite division into Eocene and 

 Miocene. We may thus have in these regions the means of 

 bridging over what has been one of the wildest gaps in the earth's 

 history and of repairing one of the greatest imperftctions in the 

 geological record. 



Physically the change from the Cretaceous to the Tertiary 

 "was one of continental elevation — drying up the oceanic waters 

 in which the marine animals of the Cretaceous lived, and afi"ord- 

 ing constantly increasing scope for land animals and plants. 

 Thus it must have happened that the marine Cretaceous animals 

 disappeared first from the high lands and lingered longest in the 

 valleys, while the life of the Tertiary came on first in the hills 

 and was more tardily introduced on the plains. Hence it has 

 arisen that many beds which Meek and Cope regard as Cretaceous 

 on the evidence of animal fossils, Newberry and Lesquereux 

 regard as Tertiary on the evidence of fossil jlants. This depends 



