428 SIE. BERNARD SMITH ON THE [Sept. 1912^ 



the development of a visible marginal drainage, chiefly because of 

 the choking and blocking of the courses previously occupied by the 

 flowing water. A further advance may then force the stream 

 to occupy a channel higher up the slope against which the ice is- 

 resting. In this case the stages of development w^ould be as- 

 follows : — after the formation of the Near-Bauk Channel the ice- 

 north of Corney Hall, advancing obliquely across the contours^ 

 caused the water to flow by way of the Corney valley and by a low 

 col at Corney Hall, that is, along two sides of a right-angled 

 triangle, of which the ice-margin formed the hypotenuse. A further 

 advance would block the Corney-Hall transverse channel and the 

 intake of the Corney Channel, and throw the water into what is- 

 now the Kinmont intake. It would then flow by way of the upper 

 half of the Kinmont Chaiinel and the Gillfoot notch into the lower 

 part of the Corney Channel, and cut that part of the latter which 

 lies south of the Corney-Hall intake. Further advance of the ice 

 would account for the excavation of the lower part of the Kinmont 

 Channel. 



This explanation, in itself, postulates that the ice, in its advance, 

 did not (althoiigh in all probability it would) fill up any of the 

 overridden channels with raorainic deposits, for they are, at present, 

 quite empty and bare. If, however, the water occupied each 

 channel a second time, during the withdrawal of the ice, it may 

 have cleared them of all obstructive material.^ In discussing, in 

 the following paragraphs, the marginal channels in the volcanic 

 tract south of Kinmont Beck, it will be seen that there is 

 reason to believe that they were chiefly cut during an oscillatory 

 retreat of the ice which followed upon a slight advance over the 

 gravels. I am, therefore, inclined to think that the main cutting 

 of the channels in the granite also was accomplished during^ 

 retreat ; but this need not prevent us from assuming that the 

 watercourses may have been first blocked out during advance. 



(ii) The Volcanic Tract east of Bootle. 



During the maximum extension of ice, the volcanic tract near 

 Bootle, together Avith those parts of the granite and slate areas 

 which immediately bound it on the north and south, were covered 

 by boulder-clay, which levelled up the hollows so that the surfaces 

 formed of dritt and solid rocks were in some cases continuous. 

 The retieat of the ice after the formation of the moraines was, as 

 before, marked by the accumulation of much fluvioglacial material,, 

 which now lies sometimes on solid rock. 



The upper limit of this drift can be traced, just below the 

 5U0-foot contour, on the lower slopes of Bootle Fell (Damkirk 

 Brow). The sands form two bold esker-like ridges (North and 

 South Coppycow) on the moorland above the 400-foot contour 

 south of Damkirk Brow, their striking shape being probably due 



^ For a description of the cutting of a complex series of marginal channels. 

 by alternations of advance and retreat, see oj). svi^^a cit. p. 130. 



