212 DR. A. JOWEIT OX THE [June I914, 



North- Western ice from, extending very high up the eastern side 

 of the valley. 



The South Lancashire and Cheshire plain on the south of the 

 Rossendale highland presented no obstacle to the North- Western 

 ice, which consequently attained a greater thickness along the 

 western slopes of the Pennines here than farther north. 



Although a great quantity of ice flowed southwards over the 

 comparatively-low ground between the Welsh hills and the 

 Pennines. the supply w T as sufficient to maintain a mass of ice over 

 1000 feet thick between the Rossendale highland and the Pennines. 

 It is also probable that the North- Welsh ice, though never directly 

 invading this area, had, by exerting a pressure from the south- 

 west, an important indirect effect in raising the level of the 

 ice-surface in South Lancashire, and thus assisting a tendency to 

 a northward and north-eastward movement. The barrier inter- 

 posed by the Rossendale hills and by the ice from the north-west 

 had effectively stopped the further progress of the Ribblesdale ice, 

 and even the stream of North- Western ice which crossed the western 

 portion of the Rossendale highland must have been weakened 

 thereby. Thus, at the time of maximum glaciation, there 

 was little to oppose the extension of the comparatively-stagnant 

 ice between the Rossendale highland and the Pennines towards the 

 north and north-east, and possibly a slight reversal of flow took 

 place where the valleys that were occupied by ice opened out upon 

 the plain. It would appear, however, that the height attained by 

 the composite ice-sheet north of the Rossendale highland was 

 greater than the height reached bv the ice on the south through- 

 out the whole period of glaciation. In the case of the Whitworth 

 valley, which was unobstructed, a definite flow northwards occurred, 

 the ice passing over the watershed, spreading over the surface of 

 the ice which had already entered the Upper Irwell Valley from 

 the west, and possibly producing a slight tendency towards a 

 westward movement, the balance between the two ice-streams 

 occurring where the Irwell Valley narrows east of Waterfoot. 

 The influence of ice-pressure from the west, as well as from the 

 south, in the Whitworth valley is indicated by the general higher 

 altitude attained by the North- Western Drift on the eastern than 

 on the western side of the valley. A similar northward-flowing 

 stream passed through the Walsden gorge, and entered the basin 

 of the Yorkshire Calder. 1 



Hence, although the greater part of the area here dealt with was 

 covered bv a confluent ice-sheet, the irregular mass of hills and 

 valleys in East Lancashire produced upon the ice an effect on a 

 much larger scale than, but otnerwise similar to, that due to a 

 number of big boulders slightly submerged in a river; the surface 

 of the ice was probably diversified with ridges and hollows, and 

 various eddies were produced within the body of the ice. Over 

 the South Lancashire plain, however, the ice-surface was doubtless 

 more uniform. 



1 J. Spencer, 'Halifax Naturalist' vol. i (1896) p. 21. 



