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crust and the core of the earth, and that some day a convulsion of the surface creates a great chasm in the crust, and the ocean rushes in and fills up part of the cavity; a tremendous quantity of steam is formed, too great to escape by the aperture through which it entered, 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.
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"It is a finely levigated silico-aluminous earth--formed by the disintegration of feldspathic or granite rocks."[1]
The particles ground out of feldspar are finer than those derived from mica and hornblende, and we can readily understand how the great forces of gravity, acting upon the dust of the comet's tail, might separate one from the other; or how magnetic waves passing through the comet might arrange all the particles containing iron by themselves, and thus produce that marvelous separation of the constituents of the granite which we have found to exist in the Drift clays. If the destroyed world possessed no sedimentary rocks, then the entire material of the comet would consist of granitic stones and dust such as constitutes clays.
The stones are reduced to a small size by the constant attrition:
"The stones of the 'till' are not of the largest; indeed, bowlders above four feet in diameter are comparatively seldom met with in the till."[2]