5 4r

CALCULATIONS TO ASCERTAIN THE TRACT

in appearance as all the other Grampian hills, a black solidstone, below the surface. There are no volcanic appearanceshere, or in any of the mountains of this county, so far as Iknow, or have been told; At the bottom of Shichallin, to agreat distance, there are lime rocks, jutting out here and there:As to plants, there are many of the Alpine kind, which growthere, and on the other moutains thereabouts, &c.” Whencewe seem authorized to infer, that the mountain consists chieflyof granitic black rock, the specific gravity of which approachesnearly to 3, that is 3 times the density of water.

Again, Mr; Playfair, the learned professor of natural phi-losophy in the university of Edinburgh has since made amineralogical survey of the hill, by which he has discovered,that the varieties of rock of which it consists, may be reducedto three kinds: a granular quartz, which occupies all themiddle part of the mountain ; a mieaceous sehistus, which en-compasses the former nearly all round like a zone to within600 feet of the bottom ; and lastly a calcareous zone, whichmay be said to surround the mountain at its base. Thoughthere is some irregularity in the disposition of these zonesjthis is at least, a general idea of the structure of the moun-tain, which does not differ greatly from the truth. By whatMr. Playfair could conjecture, the mean specific gravity ofthe whole would be about 2-7 or 2'8, one stratum being about2‘4, another about 2*75, and some rocks as high as 3, andeven 3'2. On the whole then it appears not unreasonable tosuppose the mean specific gravity of the mountain to be from2'7 to 2-75 or 2-|-. Now f x gives -§•§■ or almost 5 ; thatis, under these circumstances, the medium density or specificgravity of the whole mass of the earth, in proportion to thatof water, is nearly as 5 to 1, or that it is about 5 times theweight of water. And, with regard to this particular expe-riment, it appears that we may rest satisfied with this generalresult, drawn from' a medium specific gravity among all itsconstituent rocks. For, to have instituted a calculationfounded on an assumed distribution of the hill, in several/.ones of different densities, I am of opinion would have been