It is obvious, therefore, that when the corresponding parts are brought together, and placed in their natural order, no room is left for the reproach, that this system is inconsistent with the _existence_ of granite mountains. I have no pleasure in controversial writing; and, notwithstanding the advantages which a weak attack always gives to a defender, I cannot but regret, that Dr Hutton's adversaries have been so much more eager to refute than to understand his theory. [Illustration] 306. A remark which Dr Hutton has made on the quantity of granite that appears at the surface, compared with that of other mineral bodies, has been warmly contested. Having affirmed, that the greater part of rocks bear marks of being formed from the waste and decomposition of other rocks, he alleges that granite, (a stone which does not contain such marks) does not, for as much as appears from actual observation, make up a tenth, nor perhaps even a hundredth part of the mineral kingdom.[157] Mr Kirwan contends, that this is a very erroneous estimate, and that the quantity of granite visible on the surface, far exceeds what is here supposed.[158] The question is certainly of no material importance to the establishment of Dr Hutton's theory: it is evident, too, that an estimation, which varies so much as from a tenth to a hundredth part, cannot have been meant as any thing precise; yet it may not be quite superfluous to show, that the truth probably lies nearer to the least than the greatest of the limits just mentioned. [Footnote 157: Theory of the Earth, vol. i. p. 211.] [Footnote 158: Geol. Essays, p. 480.] 307. Though granite forms a part, generally the central part, of all the great chains of mountains, it usually occupies a much less extent of surface than the primary schistus. Thus in the Alps, if a line be drawn from Geneva to Ivrea, it will be about eighty-five geographical miles in length, and will measure the breadth of this formidable chain of mountains, at the place of its greatest elevation. Now, from the observations of Saussure, who crossed the Alps exactly in this direction, it may be collected, that less than nine miles of this line, or not above a tenth part of it, in the immediate vicinity of Mont Blanc, is occupied by granite. 308. In some sections of the Alps, no granite at all appears. Thus, in the route from Chambery to Turin, across Mont Cenis, which measures by the road not less than ninety miles, no granite is found, at least of that kind which is distinctly in mass, and different from gneiss or veined granite.[159] [Footnote 159: Voyages aux Alpes, tom. iii. § 1190, &c.]