258 Sir H. S. Hoivorth — Surface Geology of N. Europe. 



or even greater, and more insurmountable in such a case than it 

 would be in the case already cited. 



Those parts of Sweden whence the stones in question were derived 

 are so comparatively low that we cannot conceive an ice-sheet 

 existing on the scale postulated by the glacialists which did not at 

 the same time bury all such rocky surfaces fathoms deep under ice. 

 "We have already, in many ways, criticized the transcendental notion 

 involved in so-called "ground moraines," and the mechanical pro- 

 cess which the wilder American geologists euphoniously' describe 

 as " plucMng." "Plucking" is the process by which ice, under 

 a pressure of many tons to the square inch and moving so slowly 

 that the movement would be virtually inappreciable in the nether 

 layers of the ice-sheet, is supposed to have had the capacity of 

 breaking up its own bed and performing feats of quite superlative 

 dentistry. This view, which I believe to be utterly fantastic, and 

 which has never been supported by any mechanical argument or by 

 anything better than an obiter dictum, is the only refuge for the 

 believers in ground moraines as the explanation of the Swedish 

 asar. But this plucking proceeding is not all that is required. 

 Granting that we may indulge ourselves in a pIucMng theory, in 

 order to pluck up stones the ice must be in contact with its stony 

 bed, and we altogether fail even to understand the process when the 

 ice is separated from its bed by a padding of sand or gravel or 

 boulders. Can it continue to " pluck " through this intervening 

 cushion, and if so, how is it to continue doing so when the sub- 

 glacial deposit becomes 40 or 50 or a 100 yards thick ? If we 

 discard the plucking process as ridiculous, whither is the glacialist 

 to turn ? 



When a stream began to flow underneath an ice-sheet, how could 

 it possibly obtain materials from any other source to pile up a mound 

 a hundred miles long, of uniform height, and rising a hundred yards 

 above the level of the bed of the ice-sheet itself ? It could not derive 

 them from the rocks underlying its own bed, for these would be 

 protected from denudation by the sand and gravel and stones already 

 there. Suppose it were possible to get the stones (stones formed of 

 the hardest crystalline rock), how could it roll them into absolutely 

 rounded and curved forms? On such a bed basalt and gneiss are 

 not easily worn into these shapes by being rolled over beds of sand 

 and clay containing a sprinkling of stones. If it were strong enough 

 to roll them and toss them about, the subglacial stream must have 

 been a torrential river, and if so, as we have said, it must have 

 scoured out the sand and brickearth completely, instead of leaving 

 them mixed heterogeneously with the great boulders. 



I have referred to the difficulty of assigning continuous mounds 

 of the same general height and breadth, and extending over great 

 distances, to the handiwork of rivers, whose beds naturally and 

 necessarily grow wider as they march from their source to their 

 outfall ; but in the case of the Scandinavian asar the subglacial 

 theory presents an additional difficulty. According to the glacialists, 

 the Scandinavian ice-sheet extended to the Carpathians and to 



