But it would be absurd to suppose that the beds of rivers could have furnished the immeasurable volumes of gravel found over a great part of the world in the driftdeposits. And the drift-gravel is different from the gravel of the sea or rivers. Geikie says, speaking of the "till": "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." Let me again summarize : I. Comets consist of a blazing nucleus and a mass of ponderable, separated matter, such as stones, gravel, claydust, 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. *"The Great Ice Age," p. 13. 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. 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. THE HEAVENS WITH AS MUCH PROFUSION AS FISHES IN 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! Lambert regards five hundred millions as a very moderate estimate! * * Guillemin, "The Heavens," p. 251. And this does not include the monstrous fiery wanderers who may come to visit us, bringing their relations along, from outside the solar system-a sort of celestial immigrants whom no anti-Chinese legislation can keep away. Says Guillemin : "Leaving mere re-appearances out of the question, new comets are constantly found to arrive from the depths of space, describing around the sun orbits which testify to the attractive power of that radiant body; and, for the most part, going away for centuries, to return again from afar after their immense revolutions."* But do these comets come anywhere near the orbit of the earth? Look at the map on the preceding page, from Amédée Guillemin's great work, "The Heavens," page 244, and you can answer the question for yourself. Here you see the orbit of the earth overwhelmed in a complication of comet-orbits. The earth, here, is like a lost child in the midst of a forest full of wild beasts. And this diagram represents the orbits of only six comets out of those seventeen millions or five hundred millions! It is a celestial game of ten-pins, with the solar system for a bowling-alley, and the earth waiting for a tenstrike. In 1832 the earth and Biela's comet, as I will show more particularly hereafter, were both making for the same spot, moving with celestial rapidity, but the comet reached the point of junction one month before the earth did; and, as the comet was not polite enough to wait for us to come up, this generation missed a revelation. "In the year 1779 Lexell's comet approached so near to the earth that it would have increased the length of the sidereal year by three hours if its mass had been equal to the earth's." t And this same comet did strike our fellow-planet, Jupiter. "The Heavens," p. 251. "Edinburgh Review," October, 1874, p. 205. |