Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/470

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Dr. Mac Culloch on Quartz Rock.

similar investigations well know how difficult it is to ascertain the disposition of large tracts of country unless observed from situations so elevated as to raise the spectator above all the obstructions which the varying forms of high ground throw in the way of this great natural perspective. The remarks of Saussure on the highest summits of the Alps, which relate to this subject, are well known. It is not material to the purpose of determining their stratified structure, whether this stratification be continuous for a large space or whether it be various and interrupted; however desirable it might otherwise be to ascertain its disposition over the whole extent which these mountains occupy. From the low positions in which I was compelled to view those strata which I saw at hand, they appeared to be in some places horizontal, in others occupying various angular elevations, sometimes inclining to the north, and sometimes in a direction the very reverse. Such perhaps would also have been my opinion of the strata of Jura, had I not attained its highest summits. Future observers who shall ascend the Cuniack hills, the Sugar-loaf mountain, or Ben More, will be able to ascertain what I have left undone. Want of roads, want of horses, want of population, want of every thing, render this country among the most impracticable of Scotland.

The nature of this rock is exceedingly various. It is often a compact stone of a yellowish colour, and uniform texture, resembling granulated quartz, simple in its composition, and breaking with an imperfect conchoidal fracture. Occasionally it assumes a coarser and looser texture, and in these cases the weathered surface becomes white, and acquires a harsh and sandy feel and aspect. However uniform the fresh specimens appear when broken, they almost invariably disclose some internal mechanical arrangement on weathering, which betrays the nature of their original formation, a circum-