570 J. CLIFTON WARD ON THE GRANITIC, GRANITOID, AND 



been surmised from the extensive metamorphism of Skiddaw Slate 

 shown at the surface. There is certainly nothing in the lithological 

 structure or chemical composition of this granite to lead one to infer 

 that it was directly connected with the volcanic outbursts which 

 succeeded the Skiddaw-Slate period, since all the nearest lava-flows, 

 and indeed the lava-flows of the district generally, belong rather to 

 the doleritic than the trachytic or felsitic class. Whether this 

 granite was formed merely beneath the overlying parts of the Skid- 

 daw-Slate Series, or when some 12,000 feet of volcanic rocks were 

 piled above these, or, lastly, when both Skiddaw Slates and the 

 Yolcanic Series were overlain by some 14,000 feet of Upper Silurian 

 strata, it is impossible, from field-observation, to determine. The 

 widely spread and extensive metamorphism around the granite 

 seems rather to point to a deeply seated origin; and the period 

 when the lowest parts of the Skiddaw Series must have been buried 

 most deeply beneath overlying beds was the close of the Upper 

 Silurian, before that vast denudation was effected in Old Red times 

 which removed from much of the district not only all the Upper 

 Silurian strata, but all the beds of the "Volcanic Series and a con- 

 siderable thickness of Skiddaw Slates as well. 



The maximum thickness of strata under which the lower parts of 

 the known* Skiddaw Slates could have been buried is 38,000 feet; 

 and in all probability the real thickness was less than this ; of this 

 total 12,000 feetf may be put down to the Skiddaw Slates, 12,000 

 to the Yolcanic Series, and some 14,000 to the Upper Silurians. 



3. EsTcdale Granite. — The Eskdale Granite, for reasons which I 

 have briefly given in a previous paper J, and which will be entered 

 into more fully in the Second Part of this Memoir, I believe to have 

 no direct connexion with the origin of the volcanic rocks surrounding 

 it, and to have been formed, in all probability, when the topmost 

 beds of the Skiddaw Slates must have been buried beneath some 

 12,000 feet of volcanic rocks and 14,000 feet of Upper Silurian 

 strata. Since, however, the granite occurs only in the Yolcanic 

 Series, we may assign 22,000 feet as the maximum thickness of 

 rocks under which it could have been consolidated. The very 

 widely spread metamorphism of the Yolcanic Series around this 

 granite tends to negative the possibility of its having been formed 

 at the close of the Yolcanic period, before the deposition of the 

 Upper Silurian. 



4. Shop Granite. — Lastly, in the case of the Shap Granite, there 

 seems every probability that the period of its formation was the 

 close of the Upper Silurian, in which case the thickness of overlying 

 strata could not have been much more than 14,000 feet. As no 

 volcanic rocks are known to occur in connexion with the Upper 



* No base to the Skiddaw Series is seen in the district. 



•J- This is my estimate for the whole thickness known, so that it is certainly an 

 owr-estimate for that occurring aboye the granite. 



\ "The Microscopic Rock-Structure of some Ancient and Modern Yolcanic 

 Rocks," Quart. Journ. Geol. Soc. vol. xxxi. p. 388. 



