W. O. Crosby—Origin of Continents. 245 
now generally believe that the profound subsidences permitting the 
deposition of thick sedimentary formations are produced by these 
same sediments; but they rather agree with Prof. Dana that the 
oscillations are due to lateral pressure and go on independently of 
the sedimentary process. But this view certainly does not harmonize 
well with the notion that these great vertical movements of the 
crust are merely local phenomena. On the contrary, all will con- 
cede that it is more reasonable to suppose that the area affected is, 
on the average, roughly proportional to the change of level. 
Now the subsidence of 40,000 feet in the Alleghany region during 
Paleeozoic time did not make a deep ocean there, because deposition 
kept pace with the downward movement. But where is the evidence 
that the subsidence was limited to the eastern border of that great 
Paleozoic sea? Are we not, in accordance with the foregoing, at 
liberty to conclude that it affected, perhaps in equal measure, the 
central portions of the sea, where the deposition was only one-tenth 
as rapid as in the east? ‘To answer in the affirmative is to admit 
that a large part of the present continent was the site of the abyssal 
ocean. If, as we believe, the great oscillations of the crust go on 
independently of deposition, it is certainly strange that they should 
be limited to the neighbourhood of coast-lines. Prof. Dana admits 
that the important upward movements of the crust affect extensive 
areas, aS witness the elevation of North America, Europe and Asia 
in the Tertiary period, and the elevation of South America at the 
present time; and no good reason is apparent for denying that the 
same holds true with important downward movements. But specu- 
lation is unnecessary here, because the coral-islands of the Pacific 
are monuments of a subsidence which is at once profound and wide- 
spread. 
According to Prof. Dana and the great majority of geologists, the 
important movements of the crust are necessarily reciprocal, one 
part rising as the other sinks; and Prof. Dana says further that the 
oceanic crust is more flexible and rests on more mobile material 
than the continental. Why, then, should he, with the certain know- 
ledge of a Paleozoic subsidence of 40,000 feet in the Alleghany 
region, a Mesozoic subsidence of 50,000 feet in Central Europe, and 
a subsidence in the Rocky Mountains, according to King, of 60,000 
feet, etc., hold that it is extremely improbable that any part of the 
floor of the deep sea ever has been or will be elevated to form dry 
land? Again, what basis is there for the view that all extensive 
upward movements are confined to the land areas? It certainly is 
a strange doctrine that, while the stable continental crust is subject 
to repeated up and down movements of from one to ten miles, the 
(according to Prof. Dana) comparatively flexible oceanic crust is 
only susceptible of slight oscillations, in addition to a slowly pro- 
gressing subsidence covering the whole of geological time. 
As Prof. Dana has shown, however, the coral-islands testify that 
a large part of the floor of the Pacific has subsided from 38,000 to at 
least 10,000 feet in quite recent geological times. He also insists 
that this subsidence is a true downward bending of the crust, that 
