Il8 THE NEOG^IC REALM. [CHAP. 



Regarding the geological evidence of a separation between the 

 two Americas, Cretaceous marine strata occupy a large portion of 

 Mexico; and in 1879 Dr Le Conte 1 wrote as follows. The shore 

 line of the Gulf of Mexico "was much more extended both north- 

 ward and westward than either now or in Tertiary times. From 

 the Gulf there extended northwestward an immensely wide sea, 

 covering the Plains region and the Rocky Mountain region as far 

 westward as the Wahsatch range, and dividing the continent into 

 two continents, an eastern or Appalachian, and a western or 

 Basin-region continent. Probably also this sea connected across 

 the region of Mexico with the Pacific, thus dividing the western 

 continent into two, a northern and southern." Later observations 

 have shown that the Cretaceous sea undoubtedly made a wide gap 

 between North America and the southern portion of the con- 

 tinent 2 ; while the existence of Oligocene or Miocene strata in the 

 region of the isthmus of Parana shows that the separation, which 

 probably continued through the Eocene, was in existence during 



Loup-Fork in the Miocene; while to the lower part of the same era they 

 assign the John Day beds of America, and the St Gerand-le-Puy beds of 

 Europe. Others (e.g. Prof. Osborn, Studies Biol. Labor. Columbia Coll. 

 vol. i. pt. 2, p. 28, 1893) refer the Equus beds of North America to the 

 Pliocene. The following quotation from a paper by Prof. Cope (American 

 Naturalist, 1895, p. 599) conclusively proves their Plistocene age. There it 

 is stated that "the Equus beds are found covering areas of various extent in 

 Oregon, Nevada, California, the Staked Plains, Southern Texas, Chihuahua 

 and the valley of Mexico. Their most eastern station is western Nebraska. 

 They contain a fauna which includes one extinct species (Equus major Dek.) of 

 the Megalonyx fauna, and the recent Castor fiber. They contain the extinct 

 genus of sloths Mylodon, of a species different from that of the east, and four 

 species of camels of the extinct genus ffolomeniscns, and a peccary. Recent 

 species of Cam's and Thomomys occur, while two extinct horses (Equus occi- 

 dentalis Leidy and E. tau Owen) are common. The hairy elephant (E. primi- 

 genius) is abundant, while the Mastodon americanus is rare, if occurring at all. 

 The proportion of recent to extinct species and genera in the Equus bed fauna 

 is very similar to that occurring in the Megalonyx fauna, while they differ as to 

 details." 



1 Elements of Geology, pp. 451, 452, New York (1879). 



2 This separation also existed in the Jurassic era, when, as shown by 

 Neumayr (Erdgeschichte, 2nd ed. vol. II., p. 263), South America was united 

 across the Atlantic area with Africa and Madagascar. 



