PLEISTOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 449 



warmer than the present time and that the flora followed the fluctuations 

 of temperature. The plants of the Don Formation on the Don River, near 

 Toronto, Ontario,^ belong to interglacial times between the Illinoian and 

 the lowan, or even an earlier stage. The sands and clays of this formation 

 yield a flora of a climate practically similar to that of Virginia, or appre- 

 ciably warmer than that of Toronto or the northern shores of Lake Ontario 

 at the present time; in fact, it indicates that a temperature as high as that 

 of our Middle and Southern states to-day prevailed as far north as Ontario. 

 It comprises the maple (Acer), the judas tree (Cercis), the honey-locust 

 {Gleditschia) , osage orange (Madura), spruce (Picea), the hop-hornbeam 

 (Ostrya); also plane trees, poplars, plums, oaks, lindens, and elms, forests 

 such as prevail five degrees farther northward. 



In these forests of the Toronto Formation, probably belonging between 

 the Illinoian and lowan ice ages, we also find evidence ^ of the presence of 

 mammoths, mastodons, bison, deer-moose (Cervalces), and the reindeer 

 (R. caribou). 



As proof of migration we discover the cold climate fossil flora of the over- 

 lying Scarborough Beds, which indicates a return of temperature similar to 

 that of northern Lake Superior or of southern Labrador. 



The Leda Clays flora at Green's Creek on the Ottawa (central Canada 

 lat. 46° N.) is boreal rather than arctic.^ The summer temperature of this 

 period must have been somewhat cooler than at present, probably similar 

 to that of the south coast of Labrador (lat. 51° N.) to-day. The plants from 

 the Leda Clays are still found in some parts of Canada. None of them are 

 arctic. 



The most striking proof of southward migration of a northern plant is 

 that of the larch, or tamarack (Larix), discovered in Georgia (lat. 34° 30' N.), 

 or about 480 miles south of its present limit.* 



Migrations of mammals. — The extreme northward and southward 

 movements of several types of mammals in Pleistocene times along the 

 Atlantic seaboard are also very significant. Our records are chiefly con- 

 fined to the older observations of Leidy, Weigenmann, J. L. Smith, Cooper, 

 Richardson, Emmons, and Wyman. As an example of the southerly move- 

 ment of a northerly type, the walrus {Odoboenus) migrated as far south as 

 the coast of Georgia. As an example of the northerly movement of a 

 southern type, the manatee (Manatus) migrated as far north as the coast 

 of New Jersey. The caribou (Rangifer) ranged south into Pennsylvania 

 and Ohio, and we may anticipate the discovery of more southerly records. 

 The moose (Alces) is found south of the Ohio and Missouri rivers; the wapiti 



' Dawson, W., and Penhallow, D. P., On the Pleistocene Flora of Canada. Bull. Geol. Soc. 

 America, Vol. I, April. 1890, pp. 311-334; also Penhallow, D. P., Contributions to the Pleisto- 

 cene Flora of Canada. Amer. Natural., Vol. XLI, no. 487, June, 1907, pp. 443-452. 



2 Coleman, A. P., Letter to the author dated Dec. 18, 1908. 



^ Dawson, J. W.. The Geological History of Plants, 1896, pp. 218-271. 



' Chamberlin, T. C, and Salisbury, R. D., Geology, Vol. III. New York, 1906. 

 2 G 



