ve terrace from base to
apex, forming a series of steps resembling those up which the Egyptian
traveler is dragged by his guides. The human is as little disposed to look
unquestioning at these pyramidal salt-crystals as to look at the pyramids
of Egypt without inquiring whence they came. How, then, are those salt
pyramids built up?

Guided by analogy, you may, if you like, suppose that, swarming among the
constituent molecules of the salt, there is an invisible population,
controlled and coerced by some invisible master, and placing the atomic
blocks in their positions. This, however, is not the scientific idea, nor
do I think your good sense will accept it as a likely one. The scientific
idea is that the molecules act upon each other without the intervention of
slave labor; that they attract each other and repel each other at certain
definite points, or poles, and in certain definite directions; and that
the pyramidal form is the result of this play of attraction and repulsion.
While, then, the blocks of Egypt were laid down by a power external to
themselves, these molecular blocks of salt are self-posited, being fixed
in their places by the forces with which they act upon each other.

I take common salt as an illustration because it is so familiar to us all;
but any other crystalline substance would answer my purpose equally well.
Everywhere, in fact, throughout inorganic nature, we have this formative
power, as Fichte would call it--this structural energy ready to come into
play and build the ultimate particles of matter into definite shapes. The
ice of our winters and of our polar regions is its handiwork, and so
equally are the quartz, feldspar, and mica of our rocks. Our chalk-beds
are for the most part composed of minute shells, which are almost the
product of structural energy; but behind the shell, as a whole, lies a
more remote and subtle formative act. These shells are built up of little
crystals of calc-spar, and to form these crystals the structural force had
to deal with the intangible molecules of carbonate of lime. This tendency
on the part of matter to organize itself, to grow into shape, to assume
definite forms in obedience to the definite action of force, is, as I have
said, all-pervading. It is in the ground on which you tread, in the water
you drink, in the air you breathe. Incipient life, as it were, manifests
itself throughout the whole of what we call inorganic nature.

The forms of the mineral