J. D. Dana— Oceanic Coral Island Subsidence. oo 
the Rocky Mountains, Andes, Alps and Himalayas have each 
experienced since the close of the Cretaceous era, or the early 
Tertiary ; and perhaps it does not exceed the upward bulging 
in the Glacial era of part of northern North America. 
The author has presented reasons for believing* that in this 
Glacial era the watershed of Canada, between the River St. 
Lawrence and Hudson’s Bay, was raised at least 5,500 feet 
above its present level (1,500 feet); and that this plateau thus 
elevated was the origin of the great glacier which moved south- 
eastward over New England. This region is the summit of the 
eastern arm of the great V-shaped Azoic area of the continent, 
The idea that the two arms of the great Azoic V were raised 
together, is not without some support. For the courses of the 
two were the courses of great continental uplifts or movements, 
4gain and again, through the successive subsequent ages; an 
the present outline of the continent is but the final expression 
of the great fact; moreover, the elevations parallel to the 
western arm of the V have been much the greatest. Even the 
exceptional courses, such as the nearly north and south trend 
of the Green Mountains, were marked out first in the Azoic, 
ore. It is therefore reasonable that, late in geological his- 
tory, during the Glacial era, after the great mountain chains of 
* This Journal, IIT, ii, 1871. 
AM. Jour. 8ct.—Turep Series, Vou. IV, No. 19.—Jcxy, 1872. 
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