1846.] SEDGWICK ON THE SLATE ROCKS OF CUMBERLAND. 109 



I formerly explained these appearances by supposing that the altered 

 structure of the limestone or calcareous slate was due to the por- 

 phyry and felspar rock, which had burst in upon the line of the 

 limestone and separated it into two masses. New cuttings for a 

 railroad through this part of the country have given me what I 

 think a better view of its structure. I now think the porphyry (like 

 the porphyry found in some places immediately under the range of 

 the limestone) is of an older date, and that the double appearance 

 of the limestone is due to a fault. The accompanying section will 

 sufficiently explain my meaning. 



2. Section showing the reappearance of the Coniston limestone in consequence of a fault. 

 N. by W. Fault. S. by E, 



Unknown. '" -^ ^ ^^^ "^ 



The phaenomena are of great interest, but my limits prevent me 

 from giving more than this passing notice of them ; and it is obvious 

 that they involve no principle of classification affecting the fossili- 

 ferous slates. Before I quit this subject I may just remark, that 

 where the granite rises through the porphyry there are beautiful and 

 complicated mineral results. Both the porphyry and granite are 

 changed, but the demarcation may be pretty nearly traced, as the 

 main masses are not confounded. About a mile north of Shap 

 Wells the granite appears to have cut off the limestone. It is sur- 

 mounted by a micaceous glimmering slate (like that so commonly 

 seen close to the granite of Devonshire and Cornwall), which in one 

 place is riddled through by granite veins*. Farther on the ascend- 

 ing section these granular and micaceous slates appear to pass into a 

 hard splintery rock (in some places approaching the character of a 

 felstone slate) of great thickness. These hard slates are only the 

 Coniston flags (No. 2) altered by the granite, and, as is well known, 

 they are traversed by one or two dykes of red quartziferous por- 

 phyry of a later date. In the long range of the Coniston limestone, 

 from Shap Wells to the banks of the Duddon, which forms the 

 boundary of the south-west end of Cumberland, I have at present 

 nothing to add to statements given both in former papers of our 

 Transactions and in the abstract in the first volume of the Geolo- 

 gical Journal f, to which I must refer. But I was anxious to visit 

 the south-west end of Cumberland, in the hope of deciding three 

 questions. The first is, whether the Greystone House limestone on 

 the hills west of Duddon Bridge is a true Coniston limestone ? This 

 bed is underlaid by beds of schaalstein, porphyry, slate, &c. ; and 



* I believe also that the granite has pushed the upper rocks out of their hear- 

 ing, so that they are now seen to the south of the line of strike indicated by the 

 same rocks farther south-west. 



t ante cit. page 442. 



