Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/383

 of the flood was swept away ; huge rocks were torn up and were floated along, just as pine timber would have been floated in an ordinary waterway. One of these stones so floated weighs upwards of thirty tons, and is in dimensions not unlike one of the largest stones at Stonehenge. Hundreds of tons of smaller stones were torn up and swept along. Of the first mills encountered by the flood, not a vestige remains to show where they stood — the buildings, site, and subsoil (rock and shale) having been scooped out and swept away, as also the ground for a considerable distance around"

If such results followed on the sudden drainage of a small reservoir, can we believe that the water in the upper Glen-Roy lake, to a greater depth and covering nearly a hundred times the extent of surface, all passed away down a steep and by no means wide valley, without leaving behind any trace of its passage ?

The next point of supposed lake-drainage is the Pass of Maccoul, between Loch Laggan and the Spey. This pass is a narrow ravine with a flat bottom and a very slight declivity from the watershed either to Loch Laggan or the Spey. A river might thus have flowed through it without leaving any very deep trace behind. It is also much encumbered with peat, which hides and obscures the outline of the ground on which it rests. Hence though I observed no indications of an old river in this locality, I put less value on the negative evidence thus furnished. On the other hand it is curious that the river Puttaig, which falls into the pass from the south-west, and which would more naturally have flowed on to the Spey, turns sharply round and runs to Loch Laggan. Had a river from the lake flowed formerly in the other direction, we should have expected the present river to have continued its old course and not to have taken the reverse. The present channel, though not deep, is still well marked, and shows what we might have expected had a much larger river flowed in the other direction. On the other supposition of a sea-channel in this place with the western tidal currents setting through it, it is easy to see how the debris from this stream should be chiefly accumulated to the east, thus compelling the river, when the land rose out of the sea, to turn westwards to Loch Laggan. The evidence to be derived from the facts seen in this locality therefore appears to me altogether in favour of the marine theory ; but, for the reasons mentioned, I do not insist on it. This, however, is not necessary. If there is, as I have endeavoured to show, undeniable proof that no lakes ever existed so as to form the higher lines, and that these therefore must have been formed by the sea, no person will seek to ascribe a lake-origin to the lowest of the series.

There seems to me no way of meeting the evidence for the marine origin of these lines, now adduced, except either to deny that rivers flowing in such places and conditions would form such distinct and well-marked channels as I have alleged, or to affirm that such channels and other marks of their existence would soon be obliterated by subsequent changes. But, after studying the action of running water for years, both in the south and north of Scotland, I