Ixxviii PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [vol. lxxvi, 



of course, to the morainic mounds in the valleys; the roches mou- 

 tonnees ; the transported blocks ; the tarns and lake-basins ; and 

 the cwms and corries. The association of these phenomena in the 

 broader valleys was so clearly analogous to the phenomena asso- 

 ciated with the valley-glaciers of the Alps, the only form of land- 

 ice studied at close quarters in those days, that the idea of the 

 mountain-glacier became rooted as the essential explanation of all 

 our drifts ; and it has often hampered the interpretation of the very 

 ■different conditions governing the widespread glaciation of the 

 plains. However, so far as the mountain-valleys are concerned, we 

 •can generally trace in their minor features all the usual results of 

 the passage, of glaciers down them; and, even while most of the 

 valleys themselves are older than the glaciation, their present out- 

 lines owe much to the influence of the ice. Their shape has been 

 altered, in one way by the rasping-down of the solid rocks, and in 

 another way by the deposition of transported material in thick 

 masses within them, by which the actual water-channel has been 

 frequently deflected from its former position, and the stream forced 

 to carve out a second channel in the rock, beginning much above 

 the level of its previous floor. In almost every upland valley 

 within the glaciated area this deflection of the river-course is in 

 evidence somewhere or other, and has been studied and described in 

 so many instances that particularized citation is unnecessary. 



On the high ground between the valleys, where this came also 

 within the sweep of the ice, the features have probably undergone 

 less change than in any other part of our country, the chief effect 

 of the glaciation having been to clear away all the loose detritus 

 from exposed positions, redepositing some of it at high levels on 

 sheltered flats and hollows of the uplands, but conveying the larger 

 portion away from the hills altogether, so that it became mingled 

 with the drift of the plains. 



And here I may remark parenthetically upon a noteworthy cir- 

 cumstance connected with the drifts derived from the land-area in 

 England. It is the great rarity of relics of pre-existing life, 

 cither vegetable or animal, in the boulder-clays and rubble-drifts, 

 notwithstanding that they must include whatever loose material lay 

 on the old land-surface. That boulder-clay is a fairly good vehicle 

 for carrying and preserving such relics, is proved by the common 

 occurrence of marine shells, even in the .state of small fragments, 

 in all the drifts derived from the old sea-floors. Also, boulder-clay 

 is not like the fine-grained stratified sediments in which the original 



