73 



moving glacier would denude — partly by abrasion, and partly by 

 the removal of fragments of different sizes^the rocky bed over 

 which it passed. Some of the powdery material produced by 

 abrasion of the rocks lying above the sea level, would be carried 

 down by the subglacial streams to the sea. But the quantity thus 

 deposited would not be great, as the formation of this powder 

 would be mainly confined to those parts of the glacier-bed where 

 there was a sufficient quantity of water, passing down from the 

 surface of the glacier, to remove the comminuted matter as it was 

 formed. In other places, where, from the absence of crevasses, there 

 was no running water below, the accumulation of fine powder 

 would soon put an end to abrasion of the underlying rocks in the 

 same way that we know it does in certain operations in the Arts. 

 Take for instance the sharping of a joiner's chisel. But for the 

 application of oil to gather up and localise in a small compass the 

 material rubbed off the stone, the joiner would be long in edging 

 his chisel. 



Reverting to Fig. 13, between B and C the case is different. 

 The mud formed there — unlike that formed at the higher part of 

 the glacier-bed — could not be washed away by a stream, but it 

 would be squeezed out at the end of the glacier and be deposited 

 partly on the sea bottom in front, and partly beneath the floating 

 end of the glacier, so that the rock between B and C would always 

 be clean for the ice to act upon. The mud already referred to as 

 being brought down by subglacial streams from the upper end of 

 the glacier, and which would have a tendency to deposit on 

 entering the sea, owing to its motion being arrested, would also be 

 pressed out to the front of the glacier, and be deposited along with 

 the locally-formed mud. 



Many of the rocky fragments included in the glacier would be 

 similarly carried forward and deposited in the mud in front of the 

 glacier. Some of these fragments might be from the upper end of 

 the valley, and either have been torn up by the glacier from its 

 bed, or, having first fallen on to the surface of the glacier, might 

 afterwards have found their way to the bottom of it through 

 crevasses. Other fragments might remain on the surface of the 



