M. Keilhau's Theory of Granite^ and other Rocks, 95 



press themselves in an undecided and obscure manner, I really 

 do not know with certainty if any one has imagined that, for 

 example, a compact slate alone can in this manner be converted 

 into gneiss, and if a sort of smelting at the same time is assumed 

 to be also necessary. From what we have said of the theories 

 of the origin of dolomite and gypsum, it is evident that the 

 idea is current, that at least some of the component parts of 

 mineral bodies can pass through solid masses, and that they 

 can even unite with other masses in the solid form, in order, 

 in this manner, to cause the formation of new chemical combi- 

 nations, and of crystals. Although no one has thought of any 

 other mode of existence of the matter supposed to be moveable, 

 than that in the form of a gas or vapour, yet still we perceive 

 that we here find ourselves entirely on the ground we last en- 

 tered on, when we inquired after the imperfectly known modes 

 of formation of mineral species. But be the fact what it may, 

 it comes to the same thing whether we assume that these move- 

 able matters, as they are considered, are in the state of known 

 expansible fluids, or are supposed to exist in a still more subtile 

 form ; we can scarcely hope to penetrate into these mysteries, 

 and in the mean time these ideas remain alike available or alike 

 unavailable as to our problem. 



This subject ought to attract our attention in a very high 

 degree, because the outlines of the granite masses, the passage 

 of the granite into the stratified rocks at the boundary, the ra- 

 mifications we observe at other points, &c. remind us very dis- 

 tinctly that all these phenomena, even to the minutest detail, 

 are only a repetition of the appearances presented by dolomite 

 in its relations to surrounding stratified rocks. An esteemed 

 geologist, Mr De la Beche, remarks that so soon as we have an 

 accurate knowledge of the relations of position of a mountain- 

 rock, we cannot be much in doubt regarding its mode of origin. 

 I have always regarded this as an important truth, and it fol- 

 lows from it as a consecjuence, that two mountain-rocks which 

 agree in this respect, must also have had the same mode of for- 

 mation. I think, therefore, that the same theory that is ap- 

 plied to the origin of dolomite, ought also to be employed in 

 regard to granite and other analogous formations. 



The dolomite theory supposes that the dolomite has been 



