490 GEOLOGY. 



and became at length thoroughly isolated on the upper zones of the 

 mountains. On the summits of the higher peaks, such life still finds 

 suitable conditions, and stands as a living record of the former life 

 of the zone bordering the ice-sheet and surrounding the mountain 

 base. On the heights of some of the Appalachians, of Mount Washing- 

 ton, and of similar peaks, arctic plants, insects, and small mammals, 

 whose kin now live in the arctic zone, remain to this day. 



Life of the Inter glacial Stages. 



For obvious reasons very little is known of the life of the glacial 

 stages themselves, except as it is inferred from fossils found in regions 

 outside the territory invaded by the ice. The precise succession in 

 these regions, in America at least, has not yet been so closely correlated 

 with the several glacial stages as to make conclusions wholly safe. 

 The general relations of life to the adjacent ice invasions are deter- 

 minable; but as yet no systematic series corresponding in number 

 of divisions to the glacial stages has been found in orderly super- 

 position, and bearing the physical connections, or the fossils, necessary 

 for satisfactory correlation. The glacial waters were sterile, silty, 

 and cold, and hence not many fossils have been recovered from their 

 deposits at points where they are so intimately connected with the 

 ice deposits as to fix their time relations with certainty. It follows 

 that by far the larger part of the fossils whose exact relations to the 

 ice invasions can be fixed, are those which are found in the inter- 

 glacial beds. These, therefore, possess the highest order of value. 

 But even here no little circumspection is necessary to make sure that 

 the fossils were originally deposited contemporaneously with the inter- 

 glacial formations, and not introduced into them from earlier deposits 

 by ice action or interglacial wash. 



The Toronto beds. — By far the most instructive interglacial beds 

 thus far carefully studied in America are those on the Don River and 

 in the Scarboro cliffs, near Toronto, Ontario. 1 The fossil-bearing 



1 Coleman, Interglacial Fossils from the Don Valley, Toronto, Am. Geol., Vol. XII, 

 1894, pp. 86-95, with references to earlier literature, including Hinde's important 

 initial work; also Glacial and Interglacial Beds Near Toronto, Jour. Geol., Vol. IX, 1901, 

 pp. 285-310. Coleman and Penhallow, Canadian Pleistocene Flora and Fauna, Rep. 

 Com. Brit. Assoc, Bradford Meeting, 1900, pp. 328-339. Penhallow, Notes on Ter- 

 tiary Plants, Trans. Roy. Soc. Ca., Vol. X, 1904, pp. 55-76. 



