"There is something very peculiar about the shape of the stones. They are neither round and oval, like the pebbles in river-gravel, or the shingle of the sea-shore, nor are they sharply angular like newly-fallen _débris_ at the base of a cliff, although they more closely resemble the latter than the former. They are, indeed, angular in shape, but the sharp corners and edges have _invariably been smoothed away_. . . . Their shape, as will be seen, is by no means their most striking peculiarity. Each is smoothed, polished, and covered with striæ or scratches, some of which are delicate as the lines traced by an etching-needle, others deep and harsh as the scores made by the plow upon a rock. And, what is worthy of note, most of the scratches, coarse and fine together, seem to run parallel to the longer diameter of the stones, which, however, are scratched in many other directions as well."[1] Let me again summarize: I. Comets consist of a blazing nucleus and a mass of ponderable, separated matter, such as stones, gravel, clay-dust, and gas. II. The nucleus gives out great heat and masses of burning gas. III. Luminous gases surround the nucleus. IV. The drift-clays are the result of the grinding up of granitic rocks. V. No such deposits, of anything like equal magnitude, could have been formed on the earth. [1. "The Great Ice Age," p. 13.] {p. 81} VI. No such clays are now being formed under glaciers or Arctic ice-sheets. VII. These clays were ground out of the substance of the comet by the endless changes of position of the material of which it is composed as it flew through space, during its incalculable journeys in the long reaches of time. VIII. The earth-supplies of gravel are inadequate to account for the gravel of the drift-deposits. IX. Neither sea-beach nor rivers produce stones like those found in the Drift. I pass now to the next question. {p. 82} CHAPTER III. COULD A COMET STRIKE THE EARTH? READER, the evidence I am about to present will satisfy you, not only that a comet might have struck the earth in the remote past, but, that the marvel is that the earth escapes collision for a single century, I had almost said for a single year. How many comets do you suppose there are within the limits of the solar system (and remember that the solar system occupies but an insignificant portion of universal space)? Half a dozen-fifty-a hundred-you will answer. Let us put the astronomers on the witness-stand: Kepler affirmed that "COMETS ARE SCATTERED THROUGH THE HEAVENS WITH AS MUCH PROFUSION AS FISHES IN THE OCEAN." Think of that! "Three or four telescopic comets are now entered upon astronomical records every year. Lalande had a list of seven hundred comets that had been observed in his time." Arago estimated that the comets belonging to the solar system, within the orbit of Neptune, numbered _seventeen million five hundred thousand!_