THE SHAP GRANITE AND ASSOCIATED HOCKS. 293 



are vesicular throughout, and it is verified in one or two places 

 where ash-bands are interbedded with the upper part of the lavas. 

 The heterogeneous nature of the materials which constitute pyro- 

 clastic rocks makes it, however, difficult to classify them strictly 

 into families. The ashes included here have probably a composition 

 not very different from that of the andesitic lavas, and give rise by 

 metamorphism to almost identical products, but they are not very 

 sharply marked oflf from the overlying rocks which wc place in the 

 Rhyolitic Group. 



Examined at a distance from the granite, as, for example, in 

 Stockdale, the andesitic lavas are found to have suffered considerable 

 changes by the ordinary processes of weathering. These changes — 

 the destruction of the augite, the filling of the vesicles with secondary 

 products, and the formation of little veins of calcite and quartz — 

 date from a time anterior to the intrusion of the granite. This fact 

 is abundantly proved by an examination of the metamorphosed 

 rocks, and is essential to the interpretation of their phenomena. 

 It must be remembered that this part of the Volcanic Series was 

 perhaps subaerial, and rocks of this character were certainly 

 exposed to denudation while the Coniston Limestone was being 

 accumulated. 



A section of the weathered andesite of Stockdale shows crowds of 

 little felspar-prisms embedded in a pale green decomposition-product 

 which appears to represent ophitic augite. The felspar may be 

 referred by its extinction-angles to a variety near andesine in 

 composition. A few larger felspar-crystals are scattered through 

 the rock, and all are more or less turbid owing to secondary changes. 

 The pale-green mineral j)olarizes in deep indigo tints, and shows the 

 properties which seem to belong to delessite. There are none of 

 the little bastite pseudomorphs so characteristic of decomposed 

 rhombic pyroxenes in the hypersthene-andesites. There are apatite 

 prisms and a few magnetite crystals of rude form, besides a certain 

 amount of secondary magnetite-dust contained in the delessite. A 

 little dust of calcite is also present, and a considerable amount of 

 silica has been set free in the form of quartz. 



The ovoid vesicles varj- in size from one-twentieth of an inch to 

 one or even two inches. The smallest ones are filled sometimes 

 with quartz, sometimes with the pale-green product referred to 

 delessite, which has a regular radiate arrangement. Others are 

 lined with this substance, and have their interior occupied by 

 confusedly crystallized quartz. The larger ones may have detached 

 radiate aggregates of delessite in their centre, or more irregular 

 patches due to the breaking away of the lining from the wall of the 

 cavity before the silica was deposited. Other vesicles, again, are 

 partly or wholly occupied by calcite, usually in a single crystal, and 

 this kind of amygdule may often be seen side by side with the 

 others here mentioned. 



In a typical specimen of andesite taken between Wasdale Pike 

 and Great Yarlside, where the metamorphism has been but slightly 

 felt, Mr. Garwood finds 59*95 per cent, of silica. This confirms the 



