459 



families, and that whatever varieties exist in tliese respects are the 

 effects of external agencies, and the tendency to variation which 

 such agencies call into activity." 



2. On a Roche Moutonnee on the summit of the range of hills 

 separating Loch Fyne and Loch Av^^e. In a letter from 

 the Duke of Argyll to Professor Forbes. 



Polished and rounded surfaces of rock are, under their more 

 ordinary conditions, of very frequent occurrence in Argyllshire. 

 By ** their more ordinary conditions," I mean principally two — 

 viz.. Where they occur on the existing coast-line, either at, or not 

 far above the present level of the sea; secondly, Where they 

 occur in valleys, or the lower flanks of the hills, — whether under the 

 boulder clay, or on surfaces naturally exposed. 



From the occurrence on Loch Fyne of some beds of a chloritic 

 schist, which is both very soft and very tough, receiving easily 

 mechanical impressions, and resisting as easily the chemical agencies 

 which tend to wear them off, there are on its shores some very fine 

 examples of rocks rounded and deeply grooved. So far as my 

 observation goes, however, they all indicate not only a configuration 

 of the surface identical with that which now exists, but also a com- 

 paratively small change in the level of the sea. The prominent 

 points upon the shore are those which are principally marked — the 

 direction indicated is from the head of the loch towards its mouth ; 

 that is to say, the direction which ice breaking up from the high 

 mountains at the head of the lake would naturally take in its 

 passage to the open sea. There is nothing to imply a change of 

 level beyond some fifteen or twenty feet. 



In the glens leading into Loch Fyne, in the neighbourhood of 

 Inverary, the stones and boulders in the clay are abundantly marked 

 by abrading action. But I have not observed upon the walls of 

 those glens any appearances which would indicate direct glacier 

 action. When smoothed surfaces of rock appear at all, they seem 

 rather connected with the general phenomena of the Boulder Clay. 

 There is one observation, however, which applies generally, if not 

 universally, to smoothed surfaces of rock in all these situations — ■ 

 viz., that the direction of the strise is that of the glen or valley in 

 which the rock is situated, that is to say, they are in the direction 



