Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/476

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Dr. Mac Culloch on Quartz Rock.

and I can only suggest their suspicious aspect, as a reason for a further examination of them. I am inclined to entertain the same doubts relative to the quartz mountains described by authors in various parts of the world, most of which exhibit the detached and conical forms so often mentioned, and from some of which specimens have come to my hand precisely similar in their mineralogical characters to those which I have described. If such should be the fact, the necessity of finding a place for this rock in the list of formations will be more apparent than before, and it will be the duty of those geologists who lay stress on such distinctions, to ascertain the true rank it ought to bear in their system.

Schihallien.

This mountain, already highly interesting from the important geometrical operations performed on it by Dr. Maskelyne, and the subsequent mathematical computations of Dr. Hutton, has again been called into notice by Professor Playfair, in his Lithological Survey, established for the purpose of correcting the results deduced from the labours of those mathematicians.

As Mr. Playfair's remarks on the geological structure of this mountain, although chiefly referring to the particular physical object he had in view, seem to involve some important conclusions respecting the rock described in the two foregoing memoirs, I shall, I trust, be excused for stating the considerations to which they have given rise, and to which I have already alluded, since they may serve to call some further attention to its mineralogical and geological history.

The mountain itself forms the most elevated part of a ridge which may be considered as rising near Fascally, and extending in a south-westerly direction till it meets that complicated group from which