An Autobiography [151]
They are the result of the expiring energy of the volcanic discharge, which, when near its termination, not having sufficient energy to eject the matter far from its vent, becomes deposited around it, and thus builds up the central cone as a sort of monument to commemorate its expiring efforts. In this way it recalls the exact features of our own terrestrial craters, though the latter are infinitely smaller in comparison. When we consider how volcanoes are formed-- by the ejection and exudation of material from beneath the solid crust-- it will be seen how the lunar eminences are formed; that is, by the forcible projection of fluid molten matter through cracks or vents, through which it makes its way to the surface.
[Image] Pico, an isolated Lunar Mountain 8000 feet high.
It was in reference to this very interesting subject that I made a drawing of the great isolated volcanic mountain Pico, about 8000 feet high.* [footnote... this illustration exhibits a class of volcanic formations that may be seen on many portions of the moon's surface. They are what I would term exudative volcanic mountains, the results of a comparatively gentle discharge of volcanic matter, which has resulted in heaped up eminences; a vast group of which were displayed in the illustration, some of them being upwards of 20,000 feet high. ...]
It exhibits a very different appearance from that of our mountain ranges, which are for the most part the result of a tangential action. In the case of the earth, the hard stratified crust had to adapt itself to the shrunken diameter of the once much hotter globe. This tangential action is illustrated in our own persons, when age causes the body to shrink in bulk, while the skin, which does not shrink to the same extent, has to accommodate itself to the shrunken interior, and so forms wrinkles--the wrinkles of age. This theory opens up a chapter in geology and physiology well worthy of consideration. It may alike be seen in the structure of the surface of the earth, in an old apple, and in an old hand.* [footnote... The shrunken hand on the other side is that of Mr. Nasmyth, photographed by himself. According to The Psychonomy of the Hand, by R. Beamish, F.R.S., author of The Life of Sir M. I. Brunel, it exhibits a thoroughly mechanical hand, as well as the hand of a delicate manipulator; illustrating that remarkable expression in the Book of Job, that "in the hand of all the sons of men God places marks, that all the sons of men may know their own works."--ED. ...]
[Image] Shrunken Apple and Hand.* [footnote... These illustrations serve to illustrate one of the most potent of geological agencies which has given the earth's surface its grandest characteristics. I mean the elevation of mountain ranges through the contraction of the globe as a whole. By the action of gravity the former larger surface crushes down, as it were, the contracting interior; and the superfluous matter, which belonged to a bigger globe, arranges itself by tangential displacement, and accommodates itself to the altered or decreased size of the globe. Hence our mountain ranges, which though apparently enormous when seen near at hand are merely the wrinkles on the face of the earth. ...]
While earnestly studying the details of the moon's surface, it was a source of great additional interest to me to endeavour to realise in the mind's eye the possible landscape effect of its marvellous elevations and depressions. Here my artisic faculty came into operation. I endeavoured to illustrate the landscape. scenery of the Moon, in like manner as we illustrate the landscape scenery of the Earth. The telescope revealed to me distinctly the volcanic craters, the cracks, and the ranges of mountains--by means of the light and shade on the moon's surface. One of the most prominent conditions of the awful grandeur of lunar scenery is the brilliant light of the sun, far transcending that which we experience upon the earth--enhanced by the contrast with the jet-black background of the lunar heavens,-- the result of the total