f mountains being correspondent to the curves of beds which I have ever
seen; it also exhibits a condition of the summits which is of constant
occurrence in stratified hills, and peculiarly important as giving rise
to the serrated structure, rendered classical by the Spaniards in their
universal term for mountain ridges, Sierra, and obtaining for one of the
most important members of the Comasque chain of Alps its well known
Italian name--Il Resegone. Such mountains are not merely successions of
irregular peaks, more or less resembling the edge of a much-hacked
sword; they are orderly successions of teeth set in one direction,
closely resembling those of a somewhat overworn saw, and nearly always
produced by successive beds emerging one from beneath the other.

[Illustration: FIG. 18.]

[Illustration: FIG. 17.]

Sec. 22. In all such cases there is an infinitely greater difficulty in
accounting for the forms than in explaining the fracture of a single
bed. How, and when, and where, were the other portions carried away? Was
each bed once continuous over a much larger space from the point where
its edge is now broken off, or have such beds slipped back into some
gulf behind them? It is very easy for geologists to speak generally of
elevation and convulsion, but very difficult to explain what sort of
convulsion it could be which passed forward from the edge of one bed to
the edge of another, and broke the required portion off each without
disturbing the rest. Try the experiment in the simplest way: put half a
dozen of hard captain's biscuits in a sloping position on a table, and
then try, as they lie, to break the edge of each, one by one, without
disturbing the rest. At least, you will have to raise the edge before
you can break it; to put your hand underneath, between it and the next
biscuit, before you can get any purchase on it. What force was it that
put its fingers between one bed of limestone 600 feet thick and the next
beneath? If you try to break the biscuits by a blow from above, observe
the necessary force of your blow, and then conceive, if you can, the
sort of hammer that was required to break the 600 feet of rock through
in the same way. But, also, you will, ten to one, break two biscuits at
the same time. Now, in these serrated formations, two biscuits are
_never_ broken at the same time. There is no appearance of the slightest
jar having taken place affecting the bed beneath. If there be, a huge
cliff or go