226 DB. A. JOWETT ON THE [June 1914, 



(near Blackstone Edge) westwards towards the Irish Sea ; this 

 would involve the existence of an ice-sheet, rising to an altitude of 

 approximately 2100 feet above present sea-level, in the middle 

 of the Irish Sea, in the latitude of Bolton. 



Extensive systems of glacier-lakes and drainage-channels were 

 produced on the retreat of the ice. One system converged upon 

 "the Cliviger valley, by which the surplus waters on the west of the 

 Pennines, south of Boulsworth Hill, crossed the Pennine watershed 

 and escaped into the basin of the Yorkshire Calder. This con- 

 tinued until the ice had retreated so far as to expose a lower portion 

 of the Eossendale highland east of Chorley. The drainage from the 

 basin of the Ribble then escaped southwards, cutting a s} r stem of 

 large overflow-channels in this neighbourhood. 



For a long time the Irwell basin discharged its surplus waters 

 Dy way of the Walsden gorge into the Yorkshire Calder, thereby 

 giving rise to a very complicated system of overflow-channels. 



The Cliviger overflow-channel remained in use at a later stage 

 than the Walsden channel, and the evidence of the Drift-distribu- 

 "tion and the overflow-channels is in favour of a greater altitude of 

 the ice-barrier on the northern than on the southern side of the 

 Rossendale highland, at the maximum extension of the ice-sheet 

 and during all the stages of its retreat. As the ice-sheet dwindled, 

 its two components apparently separated in the neighbourhood of 

 Burnley and the North-Western ice-barrier retreated westwards, 

 while the glacier between Pendle and Boulsworth Hills retreated 

 northwards. It appears likely that the North- Western ice arrived 

 in this area later, and disappeared earlier, than the Bibblesdale ice. 

 This was doubtless owing to the fact that the former was much 

 farther from its source than the latter. 



The arrangement of the overflow-channels and of the Drift- 

 deposits indicates some slight local fluctuations in the ice-sheet, 

 but there is no evidence in this area for more than one glacial 

 period. 



In conclusion, I wish to thank Mr. S. Compston, J.P., through 

 whose kind offices I was permitted to examine and make excavations 

 in the gathering-ground of the Bury and District Joint Water- 

 Board ; also Mr. J. McV. Munro, who accompanied me on many 

 long walks over the moors ; and, above all, Prof. P. F. Kendall, to 

 whose generous help and encouragement the completion of this 

 work is largely due. 



