Mr. Hopkins's notion is simply that of the geologists. Anyone who reads his well-known papers on elevation and the formation of fissures, etc., must see that he views all elevatory forces as of liquids or quasi-liquids forced up and acting primarily _vertically_ upon the strata above them, and that these strata are not under tangential compression, but under tension. Hence the mathematical deductions contained in those papers as to the directions in which elevatory forces act, and in which fissures are formed by them, are not in any way a setting forth of such facts as occur in Nature, and, much attention as they have attracted, can only now be viewed as exercises of mathematical skill misapplied, because based upon data not to be found in Nature. In fact, those papers do but misrepresent Nature, and, like many other mathematical investigations based on untrue or insufficient data, have tended to retard knowledge. The views which I have put forward in the Paper I have referred to, read to the Royal Society, recapitulated in skeleton, so to say, are as follows. Omitting those portions which treat of our globe from the period of the first liquefaction out of a nebulous condition, and of the earliest stages of the cooling by radiation into space, when the crust was extremely thin, and of the deformation of the spheroid as one of the first effects of its contraction, and through that the general shaping out of continents and ocean beds; I have endeavoured to show that the rate of contraction of the crust, while very thin, exceeded that of the large fluid nucleus supporting it, and so gave rise to _tangential tensions_ in the crust, and fracturing it into segments; next, that as the crust thickened, these _tensions_ were gradually converted into _tangential pressures_, the contraction of the nucleus now beginning to exceed (for equal losses of heat) that of the crust through which it cooled. At this stage these tangential pressures gave rise to the _chief_ elevations of mountain chains--not by liquid matter by any process being injected from beneath vertically, but by such pressures, mutually reacting along certain lines, being resolved into the vertical, and forcing upwards more or less of the crust itself. The great outlines of the mountain ranges and the greater elevation of the land were designated and formed during the long periods that elapsed in which the continually increasing thickness of crust remained such that it was still, as a whole, flexible enough, or opposed sufficiently little resistance to crushing, to admit of this uprise of mountain chains by resolved tangential pressures. I have shown that the simple mechanism of such tangential pressures is competent to account for all the complex phenomena both of the elevations and of the _depressions_ that we now see on the earth's surface (other than continents and ocean beds), including the production of gaping fissures (in directions generally