G. W. Bulman — Formation of the Boulder-clay. 307 



scratching and polishing would be produced as the mass was moved 

 hither and thither by the flow of the ice 



Though the existence of the Moraine profonde is to a certain 

 extent hypothetical, the probability^ that such an accumulation is 

 formed beneath large ice-sheets is so great, and its character, if it 

 exists, must be so exactly that of Till, that nearly all geologists are 

 now agreed to look upon the latter as having been formed by the 

 grinding and wearing away by an ice-sheet of the ground on which 

 it rested " (p. 264). 



But as far as evidence from Greenland is available it throws as 

 little light on the origin of Boulder-clay as the Swiss valleys. Thus 

 Nordenskiold describes an area lately left by the ice as containing no 

 moraines, and in his description makes no mention of Boulder- 

 clay : " We passed, in fact, over ground that had but lately been 



abandoned by the inland ice Everywhere occur rounded, 



but seldom scratched, hills of gneiss with erratic blocks in the most 

 unstable positions of equilibrium, separated by valleys with small 

 mountain-lakes and scratched rock surfaces. On the other hand, no 

 real moraines were discoverable. These, indeed, seem to be commonly 

 absent in Scandinavia ; and are, generally speaking, more charac- 

 teristic of small glaciers than of real Inland Ice " (Arctic Voyages, 

 Macmillan, 1879, pp. 169, 170). 



And further, in describing the clay-beds of Greenland, Nordenskiold 

 speaks of them as formed outside the ice-sheet: 



" The material of the clay-beds has evidently been deposited by 

 the glacier rivers whose muddy water everywhere burst out from 

 under the inland ice, but in general the deposits are sea formations, 

 i.e. they have been deposited under the level of the sea " (Geol. 

 Mag. Vol. IX. p. 410). 



And no deposit resembling Boulder-clay is described by him as 

 occurring on that strip of Western Greenland not covered by the 

 ice-sheet at present. 



Similar remarks may be made with regard to those areas in 

 America where a retreat of the ice permits an examination of the 

 ground recently occupied by it. In the American Journal of Science, 

 March, 1892, for example, is an interesting description of Mount 

 St. Elias and its Glaciers. Where the ice has retreated glaciated 

 surfaces are seen, but no Boulder-clay. Spread out, however, over 

 the whole area between the ice and the sea is a mass of stony 

 moranic matter. Streams from the glaciers carry the finely-ground 

 rock matter into the sea. 



The probability or otherwise of the Boulder- clay having been 

 formed beneath the ice may he further considered in the light of 

 what we know of the physics of glacier action. To meet the 

 requirements of the geologist, the ice, in the form of glacier or 

 ice-sheet, must accomplish — and apparently does accomplish — a 

 variety of seemingly incompatible actions. It must clear the ground 

 of superficial accumulations and grind and polish the rock below, 

 while at the same time it must glide over loose deposits of clay and 

 stones without disturbing them ; it must round and polish certain 



