208 DE. A. JOWETT Oj* THE [June 1 9 14, 



which only boulders of local rocks occur. As one proceeds farther 

 away from the limit up to which erratics occur, the boulders of 

 local rocks are less rounded, and cease to include different types : 

 the matrix becomes more like a pulverized mass of the solid rock 

 immediately below ; and so the Local Drift passes gradually into 

 ordinary undisturbed subsoil. 



The only region within the scope of this enquiry in which the 

 subsoil is clearly undisturbed and Drift entirely absent, lies to the 

 south-west of Todmorden. Here the highest parts of the hills and 

 their north-eastern slopes appear to be devoid of Drift. 



A considerable Driftless area also occurs east of Boulsworth and 

 Black Hameldon. 



III. Evidences op Ice-action. 



In addition to the testimony furnished by the Drift with its 

 smoothed and striated boulders, and the orderly distribution of its 

 erratics, abundant evidence exists in support of the view that there 

 was once an ice-sheet in East Lancashire. Except where the 

 surface has been disturbed by recent weather and stream-action and 

 by landslips, its contours are everywhere rounded and smoothed. 

 The Drift varies in thickness, often levelling the surface by filling 

 up hollows and accumulating upon the slopes of the hills ; but the 

 hilltops and outstanding ridges are usually either bare, or have a 

 very thin covering of Drift. 



In the larger valleys and upon the plains Drift is abundant, 

 frequently presenting characteristic morainic outlines. Numerous 

 mounds occur at the Burnley entrance to the Cliviger gorge, some 

 of which are composed partly of solid rock and parti}" of Drift ; 

 but these are smoothed and rounded, so that only an occasional 

 section reveals their composite character. 



The finest series of morainic mounds in the district covers a 

 large area on the south of the Rossendale highland, stretching 

 from Bolton to Bury, Rochdale, Middleton, and North Manchester. 



Throughout the whole Drift-covered area, the details of the 

 present drainage-system are due to the blocking of the pre-existing 

 valleys by great mounds of Drift. Lakes were thus produced 

 that have been partly converted into alluvial plains, across which 

 the present streams meander, and partly drained by way of the 

 gorges that have been cut by the streams through the obstructions. 

 These gorges are sometimes cut in Drift and sometimes in the 

 solid rock, the abundance of potholes and other evidences of 

 recent and continuing rapid erosion bearing ample testimony that 

 the processes of readjustment are not yet complete. 



The positions of the several striated rock-surfaces 1 are indicated 



1 C. E. De Ranee, 'Superficial Geology of the Country adjoining' the Coasts 

 of South -West Lancashire ' Mem. Geol. Surv. 1877, p. 47 ; E. H. Tiddeman, 

 Q. J. G. S. vol. xxviii (1872) pp. 489-90 ; and H. Carvill Lewis, ' Glacial 

 Geology of Great Britain, &c.' 1894, p. 269. Mr. H. B. Maufe discovered a 

 striated surface at Rowlands, Summerseat (south of Ramsbottom), in 1901 : 

 altitude, 450 feet ; direction, north to south. 



