260 PARALLEL ROADS OF GLEN ROY chap. xiii. 



of the rivers had been made to flow east, or out of the upper 

 ends of the supposed glacier-lakes, instead of escaping at the 

 lower ends, in a westerly direction, where the great blockages 

 of ice are assumed to have occurred. 



In addition to these arguments of Mr. Jamieson, I may 

 mention that in Switzerland, at present, no testacea live in 

 the cold waters of glacier-lakes; so that the entire absence of 

 fossil shells, Avhether marine or fresh-water, in the stratified 

 materials of each shelf, would be accounted for, if the theory 

 above mentioned be embraced. 



When I examined "the parallel roads" in 1825, in com- 

 pany with Dr. Buckland, neither this glacier theory nor Mr. 

 Darwin's suggestion of ancient sea-margins had been pro- 

 posed, and I have never since revisited Lochaber. But I 

 retain in my memory a vivid recollection of the scenery and 

 phj'sical features of the district, and I now consider the 

 glacier-lake theory as affording by far the most satisfactory 

 solution of this difficult problem. The objection to it, which 

 until lately appeared to be the most formidable, and which 

 led Mr. Eobert Chambers in his " Sea Margins" to reject it 

 entirely, was the difficulty of conceiving how the waters could 

 be made to stand so high in Glen Eoy as to allow the upper- 

 most shelf to be formed. Grant a barrier of ice in the lower 

 part of the glen, of sufficient altitude to stop the waters from 

 flowing westward, still, Avhat prevented them from escaping 

 over the "col" at the head of Glen Glaster? This " col" coin- 

 cides exactly in level, as Mr. Milne Home first ascertained, 

 wMth the second or middle shelf of Glen Roy. The difficulty 

 here stated appears now to be removed by sui^jjosing that the 

 higher lines or roads were formed before the lower ones, and 

 when the quantity' of ice was most in excess. We must ima- 

 gine that at the time when the uppermost shelf of Glen Eoy 

 was forming in a shallow lake, the lower part of that glen 

 was filled up with ice, and, according to Mr. Jamieson, a 



