THE OCEANIC CORALISLAND SUBSIDENCE. A405 
thousands of feet, even thirty-five thousand by the close of the 
Paleozoic along the Appalachians, and much beyond this on 
the Pacific border; and when these thick sediments had in 
many regions been stiffened by crystallization or metamor- 
phism; I say it is reasonable that, finally, changes of level, 
through the working still of the old system of forces, should 
again have affected most the old nucleal Archzan area of the 
continent, where there had been no thickening except what 
had taken place internally; and that, if one arm of the V, 
that along the Canadian watershed, were raised at this time, 
the other, northwestern in trend, should also have been raised. 
This is at least probable enough to become a question for 
special examination over the region. See further the author's 
Manual of Geology, 1874. 
The northern continental upward movements which intro- 
duced the Glacial era, carrying Arctic cold toward the tropics, 
may have been a balance to the downward oceanic move- 
ments that resulted in the formation of the Pacific atolls. While 
the crust was arching upward over the former (not rising into 
mountains, but simply arching upward) it may have been 
bending downward over the vast central area of the great ocean. 
The changes which took place, cotemporaneously, in 
the Atlantic tropics, are very imperfectly recorded. The 
Bahamas show by their form and position that they cover 
a submerged land of large area stretching over six hundred 
miles from northwest to southeast. The long line of reefs 
and the Florida Keys, trending far away from the land of 
southern Florida, are evidences that this Florida region par- 
ticipated somewhat in the downward movement, but to a 
much less extent than the Bahamas. Again, the islands 
of the West Indies diminish in size to the eastward being 
quite small in the long line that looks out upon the blank 
