O. W. Buhnan — Formation of the Boulder-clay. 309 



be the case now, when the ice extended further and reached the 

 lakes, small bergs would be frequently detached, and melting, allow 

 their burden of stones to sink to the bottom of the lake amid the 

 clay there accumulating. 



Prof. Nordenskiold, again, has described how a similar deposit is 

 being formed in Greenland at the present day. 



" At the foot of the glacier," he writes, " we often find, as in 

 fig. 2, ponds or lakes in which is deposited a fresh-water glacial-clay, 

 containing angular blocks of stone, scattered around by small 

 icebergs" (Arctic Voyages, pp. 170, 171, Macmillan, 1879). 



But it is when we turn to the sea that we find the most 

 promising method of accounting for the origin of Boulder-clay in 

 generaL For it seems obvious that deposits analogous to Boulder- 

 clay must be accumulating on a large scale in the seas off the coasts 

 of Greenland and other ai'ctic lands. Sub-glacial rivers, laden with 

 the finer products of glaciation, are discharging themselves into the 

 sea throughout the year. Icebergs, also, are constantly being formed 

 and floated away with their loads of debris. Part of this debris no 

 doubt will be deposited only when the bergs melt in more southern 

 latitudes ; but a part will also be laid down near the coast and 

 among the finer sediment by the overturning of the bergs, which 

 not unfrequently happens. And it is, perhaps, worthy of note that 

 large quantities of glaciated stones may be carried by such bergs 

 and deposited amid accumulations of clay taking place in latitudes 

 far south of the limits of glaciation. A clay full of glaciated stones 

 may thus not necessarily imply the glaciation of the latitude where 

 it occurs. 



The opinion that the Boulder-clay was thus formed in the sea has 

 been expressed by eminent geologists. Thus Sir J. W. Dawson in 

 his " Handbook of Geology for Canadian Students," expresses his 

 opinion thus : 



(1) "Under these circumstances moraines were formed on the 

 land, and sheets of stony clay with boulders in the sea, forming 

 what has been termed the Boulder-clay or "Till" (p. 114). 



(2) " That this Boulder-clay is a sub-marine and not a sub-aerial 

 deposit, seems to be rendered probable by the circumstance, that 

 many of the boulders of the native sandstone are so soft that they 

 crumble immediately when exposed to the weather and frost " 

 (p. 154). 



And Prof. Boyd-Dawkins writes : " The hypothesis that 



the Boulder-clays have been formed on land is open to the objection 

 that no similar clays have been proved to have been so formed, 

 either in the Arctic regions, where the ice-sheet has retreated, or in 

 the districts forsaken by the glaciers in the Alps or Pyrenees, or in 

 any other mountain-chain. Similar deposits, however, have been 

 met with in Davis Strait and in the North Atlantic, which have 

 been formed by melting icebergs ; and we may therefore conclude 

 that the Boulder-clays have had a like origin " (" Early Man in 

 Britain," pp. 116, 117). 



The chief difficulty in the way of this marine origin of the Boulder- 



