THE EOCENE OF EUROPE AND NORTH AMERICA 85 



in the Upper Eocene Zeuglodon Zone ' (see p. 1 70) of Alabama and Florida, 

 and in other littoral marine deposits. 



While this vast eastern region contains no Eocene mammal-bearing de- 

 posits, it may well have been the scene of a very active continental mamma- 

 lian life from the time of the emergence of the central area toward the close 

 of the Cretaceous, or during and after Laramie time. Yet absolutely the 

 only land mammals we know from this great region up to the Pleistocene 

 are those reported by Marsh from the supposed Oligocene of New Jersey, ■ 

 namely, four species, the giant pig Entelodon, a tapiroid, Protapirus {Tapira- 

 vus) validus, a rhinoceros, Hhinoceros matutinus, and a supposed tillodont, 

 Anchippodus. The animal last named is a Rocky Mountain Middle Eo- 

 cene type, not known to have survived into Oligocene times. 



2. The plains region. — The description of this region will be deferred 

 until the introduction of the Oligocene (p. 204), with which epoch our records 

 of plains life open. 



3. Mountain region. — The mountain region contains the entire known 

 record of Eocene continental life. The mountain and high plateau region as 

 a whole stretched nearly through British Columbia to a broad land connec- 

 tion with Asia, which was aj^parently interrupted and renewed more than 

 once during the Caenozoic. On the south it terminated in the mountains 

 which form the northern boundary of the southern Mexican State Oaxaca. 

 Of the great western mountain systems of the present time the Sierra Nevada 

 range was formed at the close of the Jurassic Period, as announced by Whit- 

 ney in 1864 and confirmed by Hyatt. Only toward the close of the Creta- 

 ceous (Laramie) did the present Rocky Mountain region begin to be defined 

 by an uplift, commencing in Colorado and extending northward into Mon- 

 tana, accompanied by great volcanic outbursts, the Denver stage of Colorado, 

 the Livingston stage of IMontana, 7,000 feet in thickness on top of the Lara- 

 mie. This mountain birth, extending from Mexico on the south to British 

 America on the far north, and including a number of lesser ranges, gave rise 

 to two great geographic features, namely: the mountain basins within the 

 mountain region, and the great plains east of the mountain region, bordered 

 on the south by the gigantic Gulf of Mexico. 



In picturing in the mind's eye the mountain region in Eocene times it is 

 very important to note that the Rocky Mountain ranges were far from having 

 attained their present height; the highest emerged peaks in Eocene times 

 were beli(>vcd }\y Dana to have been perhaps 4,000 to 5,000 feet ahove sea 

 level, while the Sierra Nevada ranges at the same time were ])etween 3,000 and 

 4,000 feet above sea level. Tlie Great Basin lying bctwecMi the Rockies and 

 Sierras was probably at a heigiit of 1 ,000 feet above the sea. 



During the subsequent Cienozoic the average elevation of the Rocky 

 Mountain region was tripled, the mountain peaks in general rising from 



' Zcuolodon is an aberrant whalo-like form which probably originated in the early Eocene 

 of northern Africa. 



