That, therefore, in contracting, wrinkles (for the loftiest mountain
chains are nothing but tiny wrinkles, compared with the whole mass of
the earth), wrinkles, I say, must form on its surface from time to
time. And that the mountain chains are these wrinkles.
Be that as it may, we may safely say this. That wherever the
internal heat of the earth tends (as in the case of volcanoes)
towards a particular spot, that spot must expand, and swell up,
bulging the rocks out, and probably cracking them, and inserting
melting lava into those cracks from below. On the other hand, if the
internal heat leaves that spot again, and it cools, then it must
contract more or less, in falling inward toward the centre of the
earth; and so the beds must be crumpled, and crushed, and shifted
against each other still more, as those of our mountains have been.
But here may arise, in some of my readers' minds, a reasonable
question--If these upheaved beds were once horizontal, should we not
be likely to find them, in some places, horizontal still?
A reasonable question, and one which admits of a full answer.
They know, of course, that there has been a gradual, but steady,
change in the animals of this planet; and that the relative age of
beds can, on the strength of that known change, be determined
generally by the fossils, usually shells, peculiar to them: so that
if we find the same fashion of shells, and still more the same
species of shells, in two beds in different quarters of the world,
then we have a right to say--These beds were laid down at least about
the same time.
Pages:
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169