[Footnote 160: Dr Hutton in this case no doubt made a very loose estimate. He says, the granite does not perhaps occupy more than a 500dth part of the whole surface. The whole surface of Scotland is not much more than 23,000 geographical miles, the 500dth part of which is exactly 46; and this is exceeded by the granite in Kirkcudbrightshire done, as may be gathered from what is said § 283.] The places in Scotland where granite is found, are very well known; but the extent of some of the most considerable of them is not accurately ascertained. In the southern parts, except the granite of Galloway, which is found in two pretty large insulated tracts, there is no other of any magnitude. The granite of the north extends over a large district. If we suppose a line to be drawn, from a few miles south of Aberdeen to a few miles south of Fort William, it will mark out the central chain of the Grampians in its full extent, passing over the most elevated ground, and by the heads of the largest rivers, in Scotland. Along this line there are many granite mountains, and large tracts in which granite is the prevailing rock. There are, however, large spaces also in which no granite appears, though, if we were permitted to speak theoretically, and if the question did not entirely relate to a matter of observation, we might suppose, that, in no part of this central ridge is the granite far from the surface, notwithstanding that in some places it may be covered by the schistus. 313. A great part of the Grampian mountains is on the south side of the line just mentioned, but hardly any granite is found in this division of them, except such veins as those of Glentilt. On the north side of the line, the granite extends in various directions; and, if from Fort William a line is drawn to Inverness, the quadrilateral figure, bounded on two sides by these lines, and on the other two by the sea, will be found to contain much granite, and many districts consisting entirely of that stone. This is in fact the great granite country of Scotland: it is a large tract, containing about 3170 square geographical miles, or about a seventh part of the whole: but the proportion of it occupied by granite cannot at present be ascertained with any exactness, nor will, till some mineralogist shall find leisure to examine the courses of the great rivers, the Dee, the Spey, &c. which traverse this country. If we call it one-fourth of the whole surface, its extent is certainly not underrated, and will amount to 790 square miles nearly; to which adding 150, as a very full allowance for all the other granite contained in Scotland, exclusive of the isles, we shall have 940 square miles, between a twenty-fourth and twenty-fifth part of the surface of the whole. This computation, it must be observed, aims at nothing precise, but I think it is such, that a more accurate survey would rather diminish than increase the proportion assigned in it to the granite rock.