306 MESSRS. A. IIAHKEK AND J. E. MARE ON 



crystals of felspar, often silicified, quartz, magnetite, &c. The rolled 

 appearance of some quartz grains and other fragments seems to 

 indicate a detrital source for part of the material, and there can 

 be no doubt that most, if not all, of these rocks were formed under 

 water. 



In the ashes of the lower part of the group, the fine matrix cjicloses 

 'only a few minute grains of (juartz and occasional felspar-crystals, 

 but in some of the upper fragmental rocks of the group we find a 

 coarser-grained mass wherein identifiable fragments of minerals and 

 rocks are in excess of the matrix which unites them [1073], 

 Despite such variations as this, it will be best to consider the whole 

 of the ashes and breccias together, with respect to the effect on them 

 of the metamorphic action produced by the granite intrusion. Even 

 the rocks seen on the moorland west of the Hotel, some of which 

 would be described as ashy grits rather than ashes [1074, 1075], 

 show in their matrix the same metamorphic changes as the ordinary 

 fine-grained ashes. 



The fine ashes and the matrix of the breccias, when not exten- 

 sively altered, present the same general characters as the ashy beds 

 associated with rhyolitic lavas in other districts, such as North 

 Wales. There is usually a distinct lamination, rather wavy so as 

 to resemble a flow-structure, and this is often marked out by films 

 of a colourless or yellowish sericitic substance [706, 767]. The 

 general mass, consisting of very finely divided material probably 

 analogous to volcanic dust, offers no special peculiarities. The 

 decomposition-products are of the ordinary kind and often include 

 a considerable quantity of epidote. The embedded felspar-crystals 

 especially are in some of the rocks completely pseudomorphed by 

 aggregates of greenish-yellow to colourless epidote, but we see no 

 reason to connect this mineral with metamorpliic action in the 

 ordinary sense. More important is the formation of secondary 

 quartz in the manner already noticed in the silicified rhyolitic lavas. 

 This has taken place prior to the intrusion of the granite, and even 

 in the inner part of the contact-aureole has to a great extent pro- 

 tected the rocks so aftected from further changes. 



The metamorphism of the rhyolitic ashes is in some respects com- 

 parable with that of argillaceous strata, such as the Brathay Flags, 

 and it makes itself felt to about the same distances. The breccia 

 of the Shap Summit railway-cutting shows no decided alteration of 

 a thermo-metamorphic nature, the induration of the compact black 

 matrix being attributable to a certain formation of secondary quartz, 

 which probably took place before the date of the intrusion. This 

 is at 1400 or 1500 yards from the granite. Parther south, a 

 similar rock, though with fewer visible fragments, is exposed by the 

 side of the footpath, about 1250 yards from the granite-margin, and 

 this is within the metamorphosing influence. Under the micro- 

 scope it shows at least a superficial resemblance to the spotted 

 Brathay Flags described below in the occurrence of minute spots, 

 about jL inch in diameter, free from the brown pigment which 

 crowds most of the field [859]. The spots sometimes show between 



