REMARKS ON GLEN ROY. 9 



it, down in some places near to the shore, even in August. If three 

 times as much rain falls on Ben Nevis as there does at Laggan, 

 there is surely nothing unreasonable in assuming that the fall of 

 snow would have been in somewhat similar proportion. At all 

 events I must demur to the position that this assumption is not to 

 be made lest we offend the susceptibilities of the snow-line. ^Vhen 

 the glacial covering was in a state of full growth the whole district 

 may have been above the snow-line, but when it was in a state of 

 decay (as it evidently was at the time of the lakes) the snow -line 

 would have risen very considerably. 



III. Lake eormed during the decay oe the last Ice-sheet. 



The state of preservation of the Parallel Eoads is such that 

 it is quite clear no glaciers can have gone over them. We must 

 therefore assign their origin to a comparatively late stage of the 

 Glacial period. In another paper ^ I have endeavoured to show 

 that a great development of ice took place in Scotland after the 

 formation of those marine beds along the east coast which contain 

 Arctic shells. This last phase of the period was no time of mere 

 local glaciers issuing from a few of the higher mountains, but the 

 return of severe glacial conditions which spread over the whole 

 country : and it was during the decay of this last mantle of ice 

 that I believe the Parallel Beads were formed. I am therefore 

 unable to agree with Prof. Prestwich when he assigns them to 

 ^' a phase of the early or first Glacia;! period." ^ 



Evidently the thinner ice away to the north-east must have gone 

 off first, and that part of Scotland which lies between the Moray 

 Firth and the Pirth of Porth, round by Aberdeenshire, seems to have 

 become clear a long time before the thicker ice gave way in the 

 western glens. It was this that gave rise to the glacial lakes of 

 Lochaber. 



The same or a very similar idea has been well expressed by a 

 Norwegian geologist, Andr. M, Hansen,^ who applies it not only to 

 the explanation of certain high-lying terraces in Scandinavia, but 

 makes special reference to the Glen Poy problem. He insists that 

 it was the great decaying mass of what he calls the "inland ice," 

 and no local glaciers, that constituted the barriers of the lakes. 



ly. End op the two Upper Lines in the Ordnance Map : 

 Explanation simplified. 



At the time I wrote my previous paper on Glen Roy there was 

 •considerable uncertainty as to where the lines finally terminate. 



^ • On the last stage of the Glacial period in North Britain,' Quart. Journ. 

 Geol. Soc. vol. XXX. ( 1874) p. 317. 



2 Phil. Trans. Eoy. Soc. for 1879, vol. clxx. p. 677. 



^ ' Om seter eller strandlinjer i store hvider over havet,' Archiv for Math, 

 og IVaturvidensk. Christiania, 1885. See also letter in ' Nature,' January 21, 

 1886, p. 268. 



