[1.  “American Cyclopædia,” article “Clay.”

2.  “Edinburgh Review,” October, 1874, p. 208,

3, “Cosmos,” vol. i, p. 143.]

{p. 76}

Now, in this perpetual motion, this conflict, these great thrills of movement, we are to find the source of the clays which cover a large part of our globe to a depth of hundreds of feet.  Where are those exposures of granite on the face of the earth from which ice or water could have ground them?  Granite, I repeat, comes to the surface only in limited areas.  And it must be remembered that clay is the product exclusively of granite ground to powder.  The clays are composed exclusively of the products of disintegrated granite.  They contain but a trace of lime or magnesia or organic matters, and these can be supposed to have been infiltrated into them after their arrival on the face of the earth.[1] Other kinds of rock, ground up, form sand.  Moreover, we have seen that neither glaciers nor ice-sheets now produce such clays.

We shall see, as we proceed, that the legends of mankind, in describing the comet that struck the earth, represent it as party-colored; it is “speckled” in one legend; spotted like a tiger in another; sometimes it is a white boar in the heavens; sometimes a blue snake; sometimes it is red with the blood of the millions that are to perish.  Doubtless these separate formations, ground out of the granite, from the mica, hornblende, or feldspar, respectively, may, as I have said, under great laws, acted upon by magnetism or electricity, have arranged themselves in separate lines or sheets, in the tail of the comet, and hence we find that the clays of one region are of one color, while those of another are of a different hue.  Again, we shall see that the legends represent the monster as “winding,” undulating, writhing, twisting, fold over fold, precisely as the telescopes show us the comets do to-day.

[1.  “American Cyclopædia,” vol. iv, p. 650.]

{p. 77}

The very fact that these waves of motion run through the tail of the comet, and that it is capable of expanding and contracting on an immense scale, is conclusive proof that it is composed of small, adjustable particles.  The writer from whom I have already quoted, speaking of the extraordinary comet of 1843, says: 

“As the comet moves past the great luminary, it sweeps round its tail as a sword may be conceived to be held out at arm’s-length, and then waved round the head, from one side to the opposite.  But a sword with a blade one hundred and fifty millions of miles long must be a somewhat awkward weapon to brandish round after this fashion.  Its point would have to sweep through a curve stretching out more than six hundred millions of miles; and, even with an allowance of two hours for the accomplishment of the movement, the flash of the weapon would be of such terrific velocity that it is not an easy task to conceive how any blade of connected material substance could bear the strain of the stroke.  Even with a blade that possessed the coherence and tenacity of iron or steel, the case would be one that it would be difficult for molecular cohesion to deal with.  But that difficulty is almost infinitely increased when it is a substance of much lower cohesive tenacity than either iron or steel that has to be subjected to the strain.