D. MILNE HOME ON THE PARALLEL ROADS OF LOCHABER. 629 
Geneva, informs me by letter that its greatest length is 1400 yards ; its width 
430 yards ; and depth, next to the glacier, 114 feet. 
The Aletch Glacier, in a solid mass, flows past one end of the lake, and 
presents a wall of from thirty to forty feet above the lake, when it stands at 
its normal height, forming a solid mass of ice, therefore, of about 114 + 40= 
154 feet altogether. The normal height of the lake is determined by its 
discharge over a col, at the opposite or east end, into the Viesch Valley. 
But though this great Aletch Glacier flows past one end of the lake in a 
solid mass, does it succeed in damming the waters permanently? Berlepsh, 
in his “ Guide to the Swiss Lakes and Glaciers,” describes the Marjelen See 
particularly. He says (page 484):—“ Tous les ans, en juillet ou en aoit, le lac 
se frage un chemin, sous le glacier d’Aletch, et se verse par le Massa prés de 
Naters sur le Rhone.” 
The case of the Marjelen See, therefore, presents features which entirely 
distinguish it from Glen Roy. If even the solid body of the great Aletch 
Glacier is not sufficient to prevent the water escaping under it, how still more 
improbable would it be in the case of a dam formed by the tongue of a small 
glacier formed in a small Lochaber glen? If the solid body of the Aletch 
Glacier is unable to dam permanently a lake only 114 feet deep and 430 yards 
wide, how is it possible to suppose that merely the tongue of a glacier from the 
Treig Valley—a tongue wending its way across valleys and round hills for five 
or six miles, could dam a lake such as that which filled Glen Roy ? 
It seems really almost impossible to believe that a glacier formed in any of 
these Lochaber corries should have produced tongues of ice more than twice 
as long as the glaciers themselves, and that these tongues should, at their 
tips, have formed permanent ice barriers. ; 
Mr Jamieson brings together, to form his ice barrier for Shelf 4, no less 
than three tongues,—one from Corry M‘Eoin, one from Arkaig, and one from 
the Great Glen. The meeting of these three ice tongues, coming from opposite 
directions, would be a very remarkable conjunction indeed, if it had the effect 
of producing a solid barrier of ice ! 
(6.) All the writers who adopt the ice dam theory, feel the necessity of 
having a glacier from Loch Treig to supply a barrier for the lake in Glen Roy. 
But what if it should turn out that the Treig Valley, instead of being filled by 
a glacier at this time, was filled by water? Mr JAmrzson says, that had there 
been any of the “ Parallel Roads” in Corry M‘Eoin, from which the required 
glacier was supposed to come, he would have considered it a good objection to 
AGassiz’s ice theory (p. 246, “L. Geol. S. Journal” for 1863). 
Now, there is a Parallel Road, or what is equivalent to it, in Loch Treig. 
Sir THomas Dick Lauper says, in his Memoir (p. 43), “ Edin. R. 8. Trans.” 
vol. ix., year 1823), that the lowest shelf, called by him No. 4, as it approachcs 
