The reader will now ask, naturally enough, how such a heap of beds as
I have described can take the shape of mountains like Snowdon.
Look at any sea cliff in which the strata are twisted and set on
slope. There are hundreds of such in these isles. The beds must
have been at one time straight and horizontal. But it is equally
clear that they have been folded by being squeezed laterally. At
least, that is the simplest explanation, as may be proved by
experiment. Take a number of pieces of cloth, or any such stuff; lay
them on each other and then squeeze them together at each end. They
will arrange themselves in folds, just as the beds of the cliff have
done. And if, instead of cloth, you take some more brittle matter,
you will find that, as you squeeze on, these folds will tend to snap
at the points of greatest tension or stretching, which will be of
course at the anticlinal and synclinal lines--in plain English, the
tops and bottoms of the folds. Thus cracks will be formed; and if
the pressure goes on, the ends of the layers will shift against each
other in the line of those cracks, forming faults like those so
common in rocks.
But again, suppose that instead of squeezing these broken and folded
lines together any more, you took off the pressure right and left,
and pressed them upwards from below, by a mimic earthquake.
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