an explosion takes place, and the crust of the earth is blown into a
million fragments.

The great molten ball within remains intact, though sorely torn; in
its center is still the force we call gravity; the fragments of the
crust can not fly off into space; they are constrained to follow the
master-power lodged in the ball, which now becomes the nucleus of a
comet, still blazing and burning, and vomiting flames, and wearing
itself away. The catastrophe has disarranged its course, but it still
revolves in a prolonged orbit around the sun, carrying its broken
_débris_ in a long trail behind it.

This _débris_ arranges itself in a regular order: the largest
fragments are on or nearest the head; the smaller are farther away,
diminishing in regular gradation, until the farthest extremity, the
tail, consists of sand, dust, and gases. There is a continual
movement of the particles of the tail, operated upon by the
attraction and repulsion of the sun. The fragments collide and crash
against each other; by a natural law each stone places itself so that
its longest diameter coincides with the direction of the motion of
the comet; hence, as they scrape against each other they mark each
other with lines or _striæ_, lengthwise of their longest diameter.
The fine dust ground out by these perpetual collisions does not go
off into space, or pack around the stones, but, still governed by the
attraction of the head, it falls to the rear and takes its place,
like the small men of a regiment, in the farther part of the tail.

Now, all this agrees with what science tells us of the constitution
of clay.