244 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 21", 



On going eastward the features of a deserted river-valley increase. 

 The rocky banks recede on either side, and a flat level space occu- 

 pies the centre, now covered by peat. Beds of water-worn pebbles 

 occupy the bays and curves at the sides, and, further on, old river- 

 meadows present themselves, wdth alluvial flats running close up to 

 the rocky masses that rise abruptly from their margin, and all the 

 signs of a river-course are seen but the river itself, which has dis- 

 appeared. I quite agree, therefore, with Mr. Milne-Home, who has 

 likewise described this spot, that the evidence of a deserted water- 

 course is here very plain. 



But it will be seen, on referring to the map, that a stream called 

 the Pattag enters the head of Loch Laggan, and turns round close 

 by this watershed. It may therefore be said, admitting all this 

 evidence of a current flowing out here, might it not be merely the 

 old channel of the Pattag, that might easily be supposed, by a slight 

 diversion of its course, to have here turned eastward into the Spey, 

 instead of wheeling round, as it now does, into the head of Loch 

 Laggan ? 



The answer to this is that the deserted channel is far too large to 

 be due to a small stream like the Pattag, for it is such as a river 

 like the Spean or the Lochy might have produced. But perhaps a 

 better answer may be derived from a consideration of the old delta 

 of the Gulban already mentioned, for the height of it proves that a 

 lake must have formerly extended to Makoul, and consequently had 

 its outfall there. 



We have evidence, then, in regard to each of the Parallel Eoads, 

 that it coincides with an outlet where the water might have escaped 

 to a lower level. And, where the point has been attended to, it 

 appears that the lines just exceed the height of these outfalls suffi- 

 ciently to admit of a certain depth of water passing out. This four- 

 fold proof tells very strongly, I think, in favour of the view that the 

 lakes were freshwater. A short line which Mr. Darwin discovered 

 in a gully near Kilfinnan coincides in like manner with the water- 

 shed between it and another valley. 



The fact of the drop, or descent, of 20 or 30 feet from the Glen 

 Gluoy line to the highest one in Glen Roy has always been felt as a 

 difficulty, if we suppose the Roads to be sea-beaches ; for why should 

 there be no coincidence between the lines in these two glens, both 

 having been so favourable for the preservation of the beaches ? And 

 why, indeed, should these four lines be absent in all the other glens 

 of Scotland ? 



But Glen Roy presents an exceptional character to our other 

 mountain glens, not only in respect of its parallel roads, but also on 

 account of its great beds of silt and gravel, and, still more, the won- 

 derfully fine deltas at the mouths of its lateral ravines. All these 

 local peculiarities — the lines, the deltas, and the heavy banks of silt 

 and gravel — bespeak a local cause, such as a freshwater lake, and 

 not a universally present one like the sea. It has further been 

 pointed out, as another formidable objection to the marine theory, 

 how improbable it is that this region should have been heaved up 



