946 HISTORICAL GEOLOGY. 



in Vermont ; Arenaria Gronlandica, on the White Mountains, the Catskills, 

 Shawangunk Mountain, and, in the form of A. glabra Michx., on the Alle- 

 ghanies of Carolina ; Scirpus ccespitosus in North Carolina, a patch remain- 

 ing on Eoan Mountain, and Nei)liroma arcticum, and other northern Lichens, 

 with Lycopodium selago on the highest Alleghanies. 



Even freshwater shells of the Unio family were among the immigrants, 

 as C. T. Stimson has found by a study of fossil shells from near Toronto. 

 Scudder has shown that in North America the fossil Coleopterous Insects of 

 deposits laid down in the Glacial period are very nearly all of extinct species, 

 while those from peat beds of later origin are, with a rare exception, existing 

 species. 



The bones of the Eeindeer have occasionally been found in the valley 

 drift. Two bones, referred by Marsh to the Arctic Eeindeer, Rangifer 

 tarandus, were found in the loAver clay-beds of the Quinnipiac Eiver, three 

 miles north of New Haven, and others have been reported from near Vincen- 

 town, jST. J. Other remains, but possibly of the R. caribou, have been found 

 near Sing Sing, N.Y., in Kentucky at Big-bone Lick, and onEacket Eiver 

 in northern New York. 



The region farther south abounded, no doubt, in the beasts, birds, and 

 other species of a temperate climate. With so long a glacial front in lati- 

 tudes of 40° to 35°, at the time of greatest extension, the extreme cold 

 would have swept at times over the south, and have probably excluded 

 from the region north of Florida tropical and subtropical species, excepting 

 migrating kinds. 



Elevation of the Continent. 



The evidence that the continent, especially over its northern portions 

 and along the mountain borders, continued its rise above the sea level after 

 the Tertiary period is based largely on the facts relating to river channels, 

 fiords, and Arctic migrations between Europe or Asia and America. 



Evidence from river channels and fiords. — Near and beneath the 

 southern margin of the ice, over the interior of the continent, many river 

 channels, as proved by borings, have a depth of 100 to 400 feet below their 

 present bed. These deep gorges are filled with drift, thus making it certain, 

 that the excavation was completed in the Glacial period. Newberry states 

 that all the river valleys of Ohio are examples. The Cuyahoga, which is 

 one of them, has, where it enters Lake Erie, its bottom 200 feet below the 

 present bed, and this continues for 20 miles up the stream. The valleys of 

 northern Pennsylvania are other examples, and according to Carll and 

 White the depth of the drift-filling is, in some cases, 300 to 400 feet. At 

 the west end of Lake Ontario, the Dundas gorge has been proved by borings 

 to descend 227 feet below the sea level, or nearly half as far as the deepest 

 part of Lake Ontario, the material penetrated by the boring being drift 

 (J. W. Spencer). It is inferred that the lake was above the sea level in the 

 period, and that a river flowed along its bottom, either eastward or westward, 



