THE SHAP GRANITE AND ASSOCIATED ROCKS. 297 



portion of it within the vesicle is occupied by hornblende in crystal- 

 line continuity with tlic adjacent hornblende. 



Little magnetite-crystals are not infrequently found in the altered 

 vesicles, and sometimes pyrites. Sphene occurs in both the vesicles 

 and the narrow veins, usually in round granules, occasionally in a 

 characteristic acute-angled crystal. The metamorphic origin of all 

 these minerals is abundantly proved by their manner of occurrence. 

 In one instance only was a minute garnet found embedded in a 

 quartz within tlie vesicle [759]. 



Felspar does not appear to have been commonly formed in the 

 metamorphism of the contents of the vesicles. One slide only shows 

 good crystals of that mineral, often twinned, occupying a considerable 

 portion of some of the cavities, and accompanied by brown mica 

 instead of the customary hornblende [1203]. This specimen was 

 taken north of Wasdale Pike, about 400 yards from the nearest 

 outcrop of granite. The felspar is here moulded by the mica, and 

 occupies the marginal part of the vesicle (see PL XI. fig. 6). 



The weathered andesites before metamorphism appear to have 

 been traversed in places by little veins of chalcedony. One slide 

 [1205] shows such a vein, now transformed into quartz, but retain- 

 ing the mamillated form of deposit so characteristic of chalcedonic 

 infiltrations. Other specimens, nearer to the granite, show veins of 

 quartz-mosaic, which may or may not represent altered chalcedony, 

 but are evidently recrystallized during the metamorphism of the 

 rocks. Among other inclusions, this quartz contains minute 

 patches of brown mica with rounded outlines [1201]. 



In the field the altered andesites sometimes show silvery mica on 

 planes which seem to have been joints in the rock prior to the 

 metamorphism, — a feature observed in some other rocks near the 

 Shap Fell intrusion. 



The distribution and association of the various minerals met with 

 in the metamorphosed andesites seem to admit of a certain amount 

 of explanation on chemical grounds, supposing that the substances 

 formed at any point within the mass depended on the chemical 

 composition at that point of the weathered andesite prior to the 

 metamorphism. The phenomena described above, and especially those 

 connected with the altered vesicles, sufficiently prove that con- 

 siderable weathering had already taken place. It appears that the 

 augite had been completely, and the felspars partially, destroyed, 

 with the formation of quartz, calcite, and a chloritoid mineral as 

 the chief secondary products. In accordance with their usual 

 behaviour, the chloritoid substance was mainly in pseudomorphs 

 occupying the place of the augite, but probably disseminated also 

 through some of the larger felspars ; the secondary quartz was 

 confined mainly to the felspars ; and the calcite formed granular 

 patches or collected in veins and streaks. The vesicles were filled 

 with quartz, or with calcite and the green product, or with the 

 usual associations of these minerals, as already mentioned. 



Taking the chloritoid mineral to be delessite and the brown 

 mica biotite, the addition of some silica and the loss of most of the 



Q. J. G. S. No. 187» T 



