fully proved by the relative state of the lines and of the furrows of the torrents on the faces of the hills; namely, that its waters had once occupied a lower level, or that the valley had actually been dry before it was the receptacle of a lake. It is undoubtedly possible that the ocean might have had its various periods of elevation and subsidence, but the supposition is attended with difficulties at least as great as those which follow that hypothesis which attributes the confinement of the waters to solid and local obstacles.
It is time to conclude this subject. To those to whom even that theory which I have adopted shall appear unfounded, these reasonings can only be superfluous. To others whom such physical difficulties cannot appal, considering our limited knowledge of the present and former state of the globe, and of the actions and causes by which its present form has been produced or modified, their omission would have been unpardonable. To those who, in considering the lines of Glen Roy as works of art, are inclined to cut this knot of difficult solution, and to repose in a tacit acquiescence on motives which they are unable to appreciate, and on a state of society and manners of which history affords us no information, the whole discussion may appear unnecessary. Yet in the trust that future examinations of the earth's surface may throw future lights on this subject, and that its physical origin may be established, I shall make no other apology for the length of this paper than the extreme importance of a phenomenon which exhibits a register of revolutions in this globe of which no other similar example has yet been discovered.
