442 THE AGE OF MAMMALS 



As in Eurasia, the latest arrival in the latitude of the Middle States is 

 the northern, or hairy mammoth (E. primigenius). It is distinguished by- 

 its smaller size, its height not exceeding nine feet, by the very numerous 

 (18-27 + ) and thin plates in its grinding teeth, by its very thick covering 

 of hair and wool. 



While the characteristic geographic range of these three elephants, as 

 defined above after the studies of Lucas ^ (Fig. 189), is distinct, there are 

 points where they overlap geographically. Moreover, the teeth of the 

 northern and Columbian mammoths sometimes intergrade, so that it is 

 difficult to distinguish the species. The Columbian and imperial mammoths 

 were for a time at least contemporaneous with the mastodon, because re- 

 mains of all three species, namely, E. columbi, E. imperator, and M. america- 

 nus, have been reported^ at Afton, Iowa. E. columbi and M. americanus were 

 contemporaneous through the Central States, Missouri, Indiana, and Ohio. 

 The identification of E. imperator in these deposits is somewhat doubtful. 



Physiographic and Climatic Changes connected with Continental Elevation 



and Depression 



To understand this life and to sharply demarcate these zones we must 

 survey the series of geographic changes which marked the progress of Qua- 

 ternary times. 



As in Europe, the grand climatic changes of North America were ushered 

 in and perhaps partly caused by great changes of level which altered the 

 proportions of land and sea, and left a whole chain of biotic results in their 

 train. Briefly they were as follows: 



Elevation, beginning in the Pliocene (see p. 339) and reaching a maxi- 

 mum in late Glacial times. 

 Depression, in post-Glacial times. 

 Reelevation, to present levels. 



1. Elevation. — The seat of the North American glaciers was in 

 British Columbia from three great sources, namely: from eastern (Labra- 

 dorian), central (Keewatin), and western (Cordilleran) centers. Parts of 

 this region were elevated from 3,000 feet to 5,000 feet (Upham, 1871) 

 above the present level. 



Eastern States. — The coast of Maine rose to a height of 1,000 feet, that 

 of southern New England and as far south as Long Island, New York, to 150 

 feet. Great river channels and fiords were formed along this magnificent 

 coast line, in glacial regions only.^ See Fig. 214, p. 485. 



California. — In early Quaternary times the California coast stood from 



1 Lucas, F. A., North American Elephantids. Science, n.s., Vol. XV, no. 379, April 4, 

 1902, pp. 554-555. 



- Calvin, Samuel, Present Phase of the Pleistocene Problem in Iowa. Bull. Geol. Soc. Amer., 

 Vol. XX, Mar. 18, 1909, pp. 133-152. 



. ^ Dana, Manual of Geology, 4th ed., New York, 1894, pp. 946-949. 



