Vol. 70.] GLACIAL GEOLOGY OF EAST LANCASHIRE. 211 



A consistent explanation of the whole of these facts is by no 

 means easv to devise. If we regard the region east of Great 

 Hameldon alone, the distribution of the Drift clearly shows that 

 the Ribblesdale ice everywhere extended beyond the extreme 

 limits reached by the North- Western ice. Moreover, had the 

 North-Western Drift been deposited first, the Ribblesdale ice could 

 hardly have passed over it without destroying the North- Western 

 Drift boundary, and incorporating within itself a sufficient number 

 of north-western boulders for the deposited Drift to be of the north- 

 western type. Instead of this, boulders of the north-western type 

 are markedly absent from the Ribblesdale Drift. Yet, as already 

 urged, the movements of the Ribblesdale ice farther east clearly 

 point to the simultaneous existence of a barrier on the west ; they 

 are certainly not consistent with a complete retreat of the Ribbles- 

 dale ice, leaving the North- Western ice in possession of the field 

 when it attained its greatest development. These considerations 

 have led me to put forward the following hypothesis. 



The Ribblesdale ice advanced first, and spread its drift far 

 beyond the present limited area over which it occurs. The North- 

 Western ice then pressed up the valley between the Pendle chain 

 and the Rossendale highland as an undercurrent, practically not 

 mixing with the Ribblesdale ice, which would be raised above it 

 after the manner of a laccolite. The isolated portion of North- 

 Western Drift mentioned above might have been caught up by the 

 Ribblesdale ice, as it sheared over the underlying North- Western 

 ice, carried bodily along, and deposited within the area now covered 

 by Ribblesdale Drift. The advance of the North- Western ice up 

 the valley, by interposing a barrier where the Ribblesdale ice had 

 previously been free to move, would so tend to cut off the supply 

 of Ribblesdale ice in this locality that, when at its maximum 

 extension, the North -Western ice would only have a thin covering 

 of Ribblesdale ice, which would be practically stagnant and would 

 leave almost unfettered the movements of the more powerful stream 

 from the west. This is suggested by the shape of the North- 

 Western Drift-limit, which, especially in the vicinity of Great 

 Hameldon, clearly indicates that the Drift was deposited by ice 

 pressing in from the north-west. The distribution of the Drift 

 suggests that, while the valleys of the Limy Water and Whitewell 

 Brook were filled with Ribblesdale ice, the North- Western ice 

 pushed over the ridge south of Great Hameldon, and flowed directly 

 across the surface of the Ribblesdale ice contained in the two 

 valleys, and over the southern portion of the ridge between them. 

 The main portion of the same stream of North- Western ice flowed 

 eastwards up the Irwell Valley from Rawtenstall to Bacup, it> 

 surface, as indicated by the margin of the Drift, falling steadily in 

 that direction towards the narrowest part of the valley immediately 

 east of Waterfoot. South of Rawtenstall. the deep Irwell Valley 

 controlled a large southward-flowing stream, the hills on the west 

 reducing the pressure from that direction and preventing the 



