ce are nearly
horizontal, but there, a little way farther on, they are
perpendicular; here they are bent, and there curved; here they are
slanting, and there crushed and broken.

This only bears out what has been already said about the Book of
Geology. It _has_ been bent and disturbed, crushed and broken.

Great powers have been at work in this crust of our earth. Continents
have been raised, mountains have been upheaved, vast masses of rock
have been scattered into fragments. Here or there we may find the
layers arranged as they were first laid down; but far more often we
discover signs of later disturbance, either slow or sudden, varying
from a mere quiet tilting to a violent overturn.

[Illustration: EXAMPLE OF DISTURBANCE OF THE EARTH'S LAYERS.]

So the Book of Geology is a torn and disorganized volume, not easy to
read.

Yet, on the other hand, these very changes which have taken place are
a help to the geologist.

It may seem at first sight as if we should have an easier task, if the
strata were all left lying just as they were first formed, in smooth
level layers, one above another. But if it were so, we could know very
little about the lower layers.

We might indeed feel sure, as we do now, that the lowest layers were
the oldest and the top layers the newest, and that any fossils found
in the lower layers must belong to an age farther back than any
fossils found in the upper layers.

So much would be clear. And we might dig also and burrow a little way
down, through a few different kinds of rock, where they were not too
thick. But that would be all. There our powers would cease.

Now how different. Through the heavings and tiltings of the earth's
crust, the lower layers are often pushed quite up to the surface, so
that we are able to examine them and their fossils without the least
difficulty, and very often without digging underground at all.

You must not suppose that the real order of the rocks is changed by
these movements, for generally speaking it is not. The lower kinds are
rarely if ever found placed _over_ the upper kinds; only the ends of
them are seen peeping out above ground.

It is as if you had a pile of copy-books lying flat one upon another,
and were to put your finger under the lowest and push it up. All those
above would be pushed up also, and perhaps they would slip a little
way down, so that you would have a row of _edges_ showing side by
side, at very much the same height. The