288 _ DYNAMICAL GEOLOGY. 

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by some of the geologists who have been exploring the Western — 
Territories of America, and who point in proof of its truth to evidence _ 
of continuous subsidence in tracts where there was prolonged deposi- 
tion, and of the uprise and curvature of originally horizontal strata over 
mountain ranges like the Uintah Mountains in Wyoming and Utah, 
which have been for a long time out of water. ‘To suppose, however, 
that the removal and deposit of a few thousand feet of rock should 
so seriously affect the equilibrium of the crust as to cause it to sink 
and rise in proportion, would evince such a mobility in the earth 
as could not fail to manifest itself in a far more powerful way under 
the influence of lunar and solar attraction. That there has always 
been the closest relation between upheaval and denudation on the 
one hand, and subsidence and deposition on the other, is undoubtedly 
true. But denudation has been one of the consequences of upheaval, 
and deposition has been only kept up by continual subsidence. 
We are concerned in the present part of this volume only with 
the surface features of the land in so far as they bear on questions of 
geological dynamics. The history of these features will be more 
conveniently treated in Book VII. after the structure and history of 
the crust have been described. Before quitting the subject, however, 
we may observe that the larger terrestrial features, such as the great 
ocean basins, the lines of submarine ridge surmounted here and there 
by islands chiefly of volcanic materials, the continental masses of land, 
and at least the cores of most great mountain chains, are in the main 
of high antiquity, stamped as it were from the earliest geological 
ages on the physiognomy of the globe, and that their present aspect. 
has been the result not merely of original hypogene operations but 
of eae superficial action by the epigene forces described 
at p. 316. 
Section IV. Hypogene Causes of Changes in the Texture, 
Structure, and Composition of Rocks. 
The phenomena of hypogene action considered in the foregoing 
ages relate almost wholly to the effects produced at the surface. 
t is evident, however, that these phenomena must be accompanied 
by very considerable internal changes in the rocks which form the 
earth’s outer crust. These rocks, subjected to enormous pressure, 
have been contorted, crumpled, and folded back upon themselves, as 
if thousands of feet of solid limestones, sandstones, and shales had 
been merely a few layers of carpet ; they have been shattered and 
fractured; they have in some places been pushed far above their 
original position, in others depressed far beneath it: so ereat has 
been the compression which they have undergone that their com- 
ponent particles have in many places been re-arranged, and even 
crystallized. ‘They have here and there actually been reduced to 
fusion, and haye been abundantly invaded by masses of molten rock 
from below. 
