THE SHAr GRANITK AND \.S.sOCJATKD KOCKS. 275 



A second fault occurs at the base of the Stile End Limestone, as 

 shown by its attenuation in Stockdale and its disappearance else- 

 where; also by the change of strike in the llhyolitic Group below 

 the Stile End Limestone of Blea Beck. 



Another fault separates the Rhyolitic Group from the Andesitic 

 rocks to the north of it. The proof of this is furnished by the 

 difference of dip of the two groups on the north-east margin of the 

 granite, where the south limb of the anticline in the Andesitic 

 Group is entirely cut out. 



Besides these faults, others of minor importance cut through the 

 Rhyolitic Group to the east of the granite. Their general position 

 is shown on the map, though, owing to the quantity of drift which 

 here covers the ground, we have not been able, in all cases, to 

 indicate their exact position. 



[As the existence of these minor faults does not directly bear 

 upon the subject of this paper, we have not fully discussed the 

 evidence for their general trend and hades. We hope to recur to 

 this, however, in a future communication. — March 11th, 1891.] 



§ II. DeSCRIPTIOX 01' THE GliANITE, 



The well-known " Shap Granite ■' is familiar, not only as an 

 ornamental building-stone, but also as the material of the famous 

 boulders which have so often been made use of in tracing lines of 

 glaciation in the north of England. The most striking feature of 

 the rock is the occurrence of flesh-coloured crystals of felspar, one 

 or two inches in length, in a matrix of moderately coarse texture 

 and usually of greyish hue. In this matrix orthoclase, quartz, 

 biotite, and a striated felspar may be detected by the unassisted 

 eye or with a lens. 



In strict accuracy the name " granite " is not quite applicable to 

 the rock, which is differentiated from typical granitic rocks by its 

 porphyritic character ; but the name " granite-porphyry '' has not 

 been applied in this country except to rocks with a matrix of very 

 fine texture, and it will be sufficient to designate the Shap EeU rock 

 by its popular title, " porphyritic granite." We shall see, however, 

 that its micro-structure also presents a departure from the rules 

 which hold in most granitic rocks, the quartz being of anterior 

 consolidation to the orthoclase. 



The preponderance of felspars in the rock is partly explained by 

 its chemical composition, the silica-percentage being rather low. 

 Mr. E. J. Garwood, who has kindly made several analyses for us, 

 finds 69*78, and Dr. J. B. Cohen, in another specimen, 68*55 per 

 cent, of SiO^. The rock is thus less acid than the Skiddaw and 

 Eskdale granites, which yield 75*223 and 7y'573 per cent, of silica 

 respectively. Dr. Cohen's analysis is given on the next page (mean 

 of two) :— 



