first and highest line is to be seen in the upper Glen Roy within a very short distance of the source of the Spey, and at an elevation of some yards above the point whence the waters of this great river are directed eastwards. It is not easy to comprehend under what possible circumstances a river capable of exerting the actions required under this hypothesis, should have run towards the west. No river exists at present in the vicinity of this portion of the upper line; and even where the Roy first appears, at a place far below the position of this line, it is a feeble stream incapable of the powerful effects which must be assigned to it on this supposition.
In adducing these arguments against the present hypothesis, I may further remark, that I have given it every possible advantage by limiting the question to Glen Roy. It is easy to see that if Glen Spean and Glen Gloy, both bearing the marks of the water lines, are taken into the account, the difficulties become still more glaring.
I shall now proceed to inquire into the probabilities which attend the third and only other supposition, under which the lines of Glen Roy can be referred to the action of water. I am aware that difficulties of no trifling magnitude attend this supposition also; but none of them amount, or even approach, to physical impossibility. It is equally certain that no very direct proofs can be produced in favour of it, and that in defect of such there is nothing to offer but a set of analogies. But the strongest evidence is perhaps founded on the dilemma (to use the word in its vulgar sense) to which the whole question is reduced, in the review of the former hypotheses. At the same time it must have been apparent that the chief arguments which refer to this hypothesis have already been anticipated, since they were unavoidably implicated in the consideration of those which were used to invalidate the other two. Little therefore
