ASSOCIATED MET AMORPHIC -KOCKS OE THE LAKE -DISTRICT. 601 



in Wales, we perceive how much more the percentage of phosphoric 

 acid in the latter approaches to that of the granite (No. 6) than to 

 the metamorphosed Cumbrian ashes (JSTos. 3 and 4). Of course it 

 would be extremely unwise to conclude that the quantity of phos- 

 phoric acid found to occur in the granitic example ISTo. 6 represents 

 the proportion in the granite throughout ; what this may be, only a 

 large number of analyses can show. 



The only conclusions, therefore, that one is at all warranted in 

 drawing from the above facts are these : — 1st. That this thick series 

 of volcanic rocks contains a considerable percentage of phosphoric 

 acid ; 2nd. That since there do not occur interstratified sedimentary 

 deposits of an ordinary nature (except quite at the base), the phos- 

 phoric acid could not have been derived from such rocks immediately ; 

 3rd. That, unless derived from the Skiddaw Slates which underlie this 

 thick series of lavas and ashes, the phosphoric acid must probably be 

 considered a special constituent of the volcanic products. The 

 question whether the composition of the Skiddaw Slates is such as 

 to warrant the supposition of the phosphoric acid being derived from 

 them must be deferred to the next part of this memoir, when some 

 analyses of the slate in gradual stages of metamorphism will be 

 brought forward. 



If the granite as a mass contain so small a proportion of phosphoric 

 acid as indicated in the single example given, an additional argument 

 may perhaps be derived against the possibility of the granite having 

 been the deep-seated source from which these particular volcanic 

 rocks proceeded. 



Summary. 



1. Both observations in the field, and the examination of a complete 

 series of hand specimens of the altered volcanic rocks of Cumberland, 

 indicate the probability of a passage from such rocks into granite. 



2. The microscopic examination of such a complete series proves 

 the passage from a distinctly fragmentary to a distinctly crystalline 

 rock, and to granite itself. 



3. The chemical composition of the bulk of these volcanic rocks 

 (the ash- deposits constituting the bulk) agrees very closely with that 

 of the granite. 



4. These three points of evidence go far to prove that the granite 

 in this case may consist in great measure of but extremely meta- 

 morphosed volcanic rocks. 



5. This being a possible case (volcanic rocks + metamorphism = 

 granite), it might be argued that granite -f- communication with the 

 surface = volcanic rocks; the reasons, however, for not considering the 

 granite and volcanic rocks, in this case, to have been thus connected 

 have been already brought forward. 



6. The metamorphism around, and character of the Shap granite, 

 tend to show that that granitic mass partakes more of an intrusive 

 character, though much of the matter of the volcanic rocks immedi- 

 ately surrounding may have been partly incorporated with it, es- 

 pecially near the margins. 



