44 Merriam Geographic Distribution of Life. 



Great Basin " shows two lacustral epochs corresponding to 

 two glacial epochs, and correlates the mammalian fauna with 

 the later half of the later Glacial epoch. Presumptively this 

 date falls very late in -the Pleistocene period." (Lake Bonnc- 

 vffle, by G. K. Gilbert, 1890, 397.) The mammalian fauna 

 referred to comprises an elephant, an otter, two horses, three 

 llamas, a deer of the genus Cervus, an ox, a gigantic sloth, 

 together with three species now living, namely, the coyote, 

 beaver, and pocket gopher (Thomomyii). No new types came in 

 to take the place of those exterminated; hence we in the 

 United States now live in a region deprived of many of the 

 groups to which it gave birth, and we are forced to visit remote 

 parts of the earth to see animals and plants that once attained 

 their maximum development in North America, while others 

 that formerly flourished here are entirely extinct. 



Not only are the pre-Pleistocene animals and plants now 

 represented imperfectly and in greatly reduced numbers, but 

 the areas at present inhabited by their descendants, except in 

 the case of the Boreal forms, are insignificant in comparison 

 with their former extent. It should be remembered that the 

 refrigeration of the Glacial epoch has only in part disappeared. 

 In early Pliocene times characteristic representatives of sub- 

 tropical faunas and floras existed northward over much of the 

 United States and Canada, and in still earlier times reached the 

 Arctic Circle.* During the advance of cold in the Glacial 

 epoch these forms were either exterminated or driven south- 

 ward into the narrow tropical parts of Mexico and Central 

 America. The retreat of cold at the termination of this period 

 was not complete, and our continent has never regained its 

 former warmth. Hence the expelled species were not per- 

 mitted to advance more than a short distance into the region 

 formerly occupied by them, and the tropical species have been 

 held back and at the present day are not found except along 

 the extreme southern confines of our territory. For example, 

 peccaries in early Pleistocene times ranged northward over 

 a large part of western America, while at present they are 

 restricted to parts of Texas and Louisiana below the Red River 

 of the South; and the capybaras, tapirs, and other tropical 



* Among trees fossil remains of magnolia, sassafras, and liquidamber 

 have been found in Greenland. 



