Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/345

 side, which according to my information extends far towards the bottom of the glen, and is therefore continuous with that one which I examined from its mouth. The principal question with regard to this line is, whether it corresponds with the uppermost or with the second of Glen Roy. I attempted to determine it by the spirit level and by the barometer. The former observations were so much impeded by the weather that I am unwilling to place any reliance on them, since the vertical difference of these two lines being little more than 80 feet, considerable nicety would be required in carrying on the levels. From the barometric observations it appears that the difference of level between this upper line of Glen Gloy and that of Glen Roy is only 12 feet, a difference that may fairly be attributed to errors of observation. It is probable therefore that these two are on the same level, while there seems abundant reason to conclude, from the general similarity of proportion between the intervals of those in Glen Gloy and those in Glen Roy, that the former have originated from the same cause as the latter, and admit of the same general train of reasoning which will hereafter be applied to these. If any doubt should remain, in consequence of the want of more positive evidence, it must be remembered that the lines of Glen Roy have been shown to enter Glen Spean, and also to be prolonged through the common wide valley in which both these rivers terminate; that the situation of Glen Gloy is by the intervention of Glen Lochy analogous to that which Glen Roy holds to the common valley of the Spean and Roy; and that on a calculation of chances it is almost infinitely improbable, that the apparently corresponding proportions of the three lines of Glen Gloy are not actually corresponding, and sufficient to prove, if not a former continuity between the levels of the different vallies, at least a common cause for all.