•Vol. 70.] GLACIAL GEOLOGY OF EAST LANCASHIRE. 201 



Grit and Coal Measures. In a few localities, the sandstone, shale, 

 and impure limestone of the Pendleside Series crop out. Where 

 the Drift contains boulders of the above-mentioned rocks only, it 

 will be termed Local Drift. 



When, in addition to the above, boulders of Carboniferous Lime- 

 stone and chert, and Silurian grit- and slate, doubtless chiefly 

 derived from the exposures of such rocks in Ribblesdale and the 

 adjoining parts of the Pennines, occur in the Drift, it will be 

 alluded to as Ribblesdale Drift. 



In the most complex type, 1 many rocks from the Lake District 

 and some from the South of Scotland occur, together with any or 

 all of the varieties already mentioned ; this type will be termed the 

 North-Western Drift. 



It should be understood that each of these three types may 

 include Drift of varying texture. 



(c) The Distribution of the Three Types of Drift. 



Mr. R. H. Tiddeman 3 first pointed out that in Ribblesdale a 

 boundary might be drawn between the ' Lake-country drift ' and 

 the 'local drift,' which is here termed the Ribblesdale Drift. 



As the boundaries between the three types of Drift in this part 

 of Lancashire occur for the most part on high moorland that is 

 intersected by many natural and artificial watercourses, it has been 

 found possible to trace them with considerable precision, and on the 

 accompanying map (PL XXXIII) they are indicated as reduced 

 from maps on the scale of 6 inches to the mile. The map also 

 summarizes a great many records of boulders and Drift sections 

 throughout the area. The method adopted has been to examine the 

 superficial deposits wherever they are exposed, especially the 

 continuous sections in the gently-sloping channels that have been 

 cut in order to drain the moors. Following such a section up hill, 

 one commonly finds the erratics becoming; continuously less 

 abundant until perhaps only two or three occur in a distance of 

 50 yards, and, farther up the stream, they cease altogether. The 

 general appearance of the Drift, however, remains unaltered in other 

 respects for some considerable distance. Thus, Ribblesdale Drift or 



1 The following list of boulders obtained in "Wellington Road, Bury, is given 

 as an example of the variety of rocks that may be found in a single section 

 of North-Western Drift : — Grey granite, probably from Criffel (Scotland). 

 Granites from Shap (Westmorland), found by Mr. H. B. Maufe, and Eskdale 

 (Cumberland). Hornblende - syenite. Granophyre from Buttermere and 

 Ennerdale. Three distinct types of quartz-porphyry. Pink, white, and green 

 varieties of rhyolite. Many types of andesite, one much sheared. Yewdale 

 andesitic breccia. Chalk flints. Limestone breccia with red matrix ; probably 

 Brockram. Silurian grit, probably from the Northern Pennines. Greywacke 

 grit, probably from the South of Scotland. Quartzite. Vein-quartz with 

 haematite. Carboniferous Limestone with Lithostrotion and encrinites. Chert 

 full of casts of large encrinites ; banded chert. Millstone Grit. Coal-Measure 

 sandstone and shale ; Gannister ; coal. 



3 • On the Evidence for the Ice-Sheet in North Lancashire, &c.' Q. J. G. S. 

 vol. xxviii (1872) p. 485. 



p2 



