280 MESSES. A. HARKER AND J. E. MARK ON 



also exceptional in that its quartz crystallized prior to the final 

 consolidation of the rock. If we suppose this mineral to have been 

 brought up by the magma from its place of consolidation at a greater 

 depth, the difficulty vanishes. 



One of the most striking characters of the Shap Fell granite s 

 the occurrence of distinct patches of darker colour and somewhat 

 finer texture than the surrounding rock. These patches are abundant 

 in the quarries, and may be well studied in the polished slabs and 

 pillars used in building *. They are of rounded outline, though not 

 usually spheroidal, and have a sharply defined boundary. Most of 

 them are only a few inches to a foot or two feet in diameter, but 

 there is one large enough to be separately quarried for setts. They 

 contain, though rather more sparsely, porphyritic felspars like those 

 of the normal granite ; and Mr. Phillips gives instances of felspars 

 lying partly in the dark patches and partly in the surrounding rock. 

 The large felspars within the inclusions frequently have, however, 

 a rather rounded outline, and present other peculiarities which will 

 be described below. 



It is evident that these phenomena cannot be explained by sup- 

 posing the liquid granite to have caught up fragments of rocks 

 broken through in its irruption and metamorphosed them to a 

 crystalline condition. There are, indeed, some inclusions in the 

 granite which represent highly altered fragments, but they are much 

 less common than the type under consideration. They show a closer 

 texture, and never enclose porphyritic felspars. Further, their form 

 is quite irregular, and usually angular, and one large specimen in 

 the Woodwardian Museum has evidently been a shaly or slaty rock, 

 which has been partly split and penetrated by tongues of granite in 

 the direction of its laminae. 



Leaving out of account evident included fragments, we have a type 

 of inclusion possessing very definite characters, and agreeing with 

 what is observed in many other granites, granophyres, and syenites. 

 The inclusions are constantly of finer texture, greater density, darker 

 colour, and more basic composition than their matrix. In the 

 following table of silica-percentages the figures for the Shap Pell 

 rock are obtained from Mr. Garwood, those for the other granites 

 being quoted from Mr. J. A. Phillips's paper : — 



Matrix. Inclusion. 



Gready, Cornwall 69-64 65-01 



Peterhead 73-70 64-39 



Ardshiel (Fort William) — 52-43 



Shap Fell 69-78 56-95 



It will be seen that the difference between matrix and inclusion 

 is greater in the Shap Fell granite than in those of Gready and 

 Peterhead. 



An average specimen of an inclusion from the Shap quarries was 

 found to have a specific gravity of 2*769. This is considerably 



* E. (j. at the Midland Grand Hotel, St. Pancras Eailway Terminus. 



