valley might have to be filled, though the ridge might have to be
surmounted, still the general tendency of the waves would be to level
the dropping deposits into flat layers.

Then how is it that when we examine the strata of rocks in our
neighborhood, wherever that neighborhood may be, we do not find them
so arranged? Here, it is true, the lines for a space 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