404 CORALS AND CORAL ISLANDS. 
the more central portions of the continent :—we cannot say 
western portions also, since in the first place, the facts, accord- 
ing to Prof. J. D. Whitney, do not sustain the statement ; and, 
in the second, the great mountain ranges of the west would 
have been a barrier to all influences from any central conti- 
nental elevation, and, besides, the slopes of these ranges, even if 
the Pacific border were higher to the north than now, would 
have determined the course of all western glacial movements. 
The idea that both arms of the great Archzean nucleus were 
raised together, is not without some support. For the courses of 
the two were the courses of great continental uplifts or move- 
ments, again and again, through the successive subsequent ages; 
and the present outline of the continent is but the final expres- 
sion 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 Archzean, the 
Archzean peninsula of northern New York with the line of the 
Adirondacks being an exhibition of it. And all this uniformity 
of movement, from the laying of the first stone in the develop- 
ing continent to the last, has been shown by the author to be 
directly connected with the fact that the continent has always 
been bordered by the same two great oceanic depressions, the 
Atlantic, and the larger Pacific, the same in trend of axis as 
now, the North Atlantic having a northeast and southwest 
trend, parallel with one arm of the Archean, and the Pacific 
a northwest and southeast parallel with the other arm of the 
Archean. It is therefore reasonable that, late in geological 
history, during the Glacial era, after the great mountain chains 
of the continent had been made and raised to their full height, 
and the surface crust thickened over all the continent, except 
that of the Archzan nucleus, by successive beds to a thickness of 
