hollows of our mountain lakes, which many of them resemble, if we imagine a sandy plain at the bottom instead of water. When there is a central mountain, its shadow is distinctly cast upon this plain, by which its shape can be ascertained and sketched, and its height measured trigonometrically.*

Thus are we led to perceive, that while our satellite possesses some features in common with her primary, the nature and general distribution of her surface is very different.

There have been many speculations upon the cause of this singular crateriform structure, of which the earth seems to afford but comparatively few analogous specimens. The natural and usual solution of the question, however, hitherto received has been, that it owes its origin to volcanic force, of a similar nature to those in operation upon our own globe; and that Etna, Vesuvius, Teneriffe, and Hecla, together with the other active or inactive cones of disturbance, are the types of the lunar, which they seem to resemble in many particulars; only instead of being confined to a few points, as here, they operated universally over the lunar surface, as we should find was probably the case upon the earth before her sedimentary deposits had covered, as with a garment, the naked and torn bosom, now so fertile; which was designed to be afterwards a habitation for God's last and greatest work.

I am inclined to think (though, of course, it is a question that does not admit of positive proof) that this is the true history

* Appendix C.

C

of lunar disturbance, although it must have been of a peculiar character, and of a very violent nature. A remarkable evidence of this, indeed, is afforded by a peculiar feature in lunar scenery. There are some of her craters to which the name radiating has been given, from the appearance of straight, white lines, which radiate from them in every direction, like the glory round the head of saints, and extend, some of them, to a vast distance across the surface of the planet-sometimes crossing each other, but pursuing their course, like our railroads, only accommodating themselves to the nature of the ground, without suffering anything to impede them or turn them aside into the slightest curve; now ascending mountains, and now descending into the very bottom of craters, cutting them, as it were, in two, without the least deviation. One of these remarkable lines can be perceived with the naked eye, proceeding from the crater called Tycho, situated in the southern portion of the moon's hemisphere, where, probably, the greatest disturbance has taken place, and where craters and mountains are crowded upon one another, in wild and terrible profusion. This line that thus radiates from Tycho (which is a vast, deep crater, with a central mountain, and a chasm fifty-five miles across) spans nearly the entire disc of the moon; and can be perceived with a telescope, as a white, shining line, crossing the Mare Serenitatis, having run a course of nearly 1,700 miles! The full moon is the best period for observing these rays, which, as they generally throw no shadow, have somewhat perplexed astronomers.

The

*

explanation usually given, however (which is probably the truth), is, that these radiating craters were successively the centres of a terrible convulsion, which operated on the crust of the moon as the blow of a stone would upon a piece of plate-glass, sending out sloping but elevated ridges in all directions from the centre of disturbance.

* As the rays from different craters cross each other, they are observed to eclipse, or conceal one another at the points of intersection, evidently according to the age or chronological era of the crater, whose rays thus, like the hands of a clock, point out the order and time of the successive eruptions-and, probably, the original formation of each crater. Professor Nichol thus clearly explains this theory :-" If a ray or vein from one granite cuts the vein of another granite, we instantly infer the posteriority of the former. Now, I find that rays from Kepler cut through rays from Copernicus and Aristarchus, while rays from Aristarchus also cut through rays from Copernicus; there is, therefore, no doubt whatever as to the ages of these interfering streams. They stand in this order-Copernicus, Aristarchus, Kepler."- Nichol on the Solar System, p. 165.