It is easy to comprehend that these are the remains of such deltas or alluvia, undermined during the different subsidences of the lake, and remaining as indications of their former existence.
Having now compared all the appearances of Glen Roy with those which are to be found in existing lakes, and considered the probable changes which the drainage of such lakes would effect on their containing valleys, I shall proceed to point out the difficulties with which even this hypothesis is encumbered.
It has been seen in the description, that considerable deficiencies may be observed in the courses of these lines, as well in Glen Roy itself, as in the neighbouring glens. Some of these anomalies indeed assist in proving the probability of the hypothesis here considered the remainder, yet unaccounted for, may perhaps be explained hereafter, when observations have been further multiplied. One short line only, is found in the upper valley of Glen Roy; yet all the sides exhibit a general equality of slope, form, and texture; nor is any side more than another, subject to the action of a visible wasting cause. A great deficiency of the whole of the lines occurs also towards the bottom of lower Glen Roy, and many partial ones in other places. Of these, some evidently arise from the rocky nature of the margin, and others may perhaps be the consequence of the coincidence between the slope of the hill and the slope of the supposed shore. But these causes will not account for them all, nor are there sufficient marks of the action of posterior waste to explain them. The anomalies of Glen Gloy and Glen Spean in particular, which I have described at length in the commencement of this paper, seem at present to baffle all explanation, and in this unsatisfactory state must the argument remain. It were well if there were no further difficulties to encounter in adopting this hypothesis, but it is necessary to enumerate them.
