344 KEV. E. HILL AND PKOF. T. G. BONNET ON THE 



broken . The large grains of epidote are obviously of secondary forma- 

 tion ; from their octagonal outline and angles we may, in two cases, 

 safely assert the original mineral to have been augite ; viridite ap- 

 pears, both associated with it and alone, probably also replacing a 

 kindred mineral. 



Slides cut from the rock at the base of Peldar Tor, from the 

 Sharpley-like rock in the Bardon-Hill pit, and from the outcrops 

 mentioned above have been carefully studied : their differences from 

 the above are merely varietal ; and the green rock at the base of 

 Eatchet Hill, though containing a little more viridite, is in all 

 essential points identical. 



The question, then, we have to answer is : Are these rocks lavas ? 

 and if not, how is their porphyritic structure to be explained ? Cer- 

 tainly they are not unlike lavas ; the cryptocrj^stalline ground-mass, 

 the included crystals, would not ill agree with a devitrified rhyolite 

 such as we can examine in the Wrekin district, or between Caernarvon 

 and Eangor. Still, on closely studying the ground-mass of these 

 Sharpley rocks, we note various minute points of diiference, such as an 

 indefiniteness of structure, a suggestion here and there of fragments, 

 which seem to separate them from every undoubtedly igneous rock 

 which we have studied. The persistent schistose character of the 

 rocks over so large an area is also most difficult to explain on that 

 supposition. So also is the gradual passage of the undoubtedly 

 fragmental bands (in the southern ridge) into the normal rock. 

 "Were the latter a lava, the line of demarcation between it and 

 the ash -bands should be a definite one, and be detected without 

 much difficulty, as the rock-surfaces exposed are favourable to 

 examination. After repeated study in the field and with the 

 microscope, and comparisons with numerous type specimens, we 

 cannot alter our original opinion that these rocks of High Sharpley 

 are not lavas. 



We are then called upon to explain their porphyritic structure. 

 The quartz and felspar grains closely resemble those occurring in 

 many other Charnwood rocks which undoubtedly are of clastic 

 origin ; they also resemble them in having clear, sharp boundaries, 

 even when broken. There is not that indefiniteness of outline 

 and appearance of melting away (as it were) into the surrounding 

 ground-mass which commonly characterizes crystals (especially of 

 felspar) when developed in situ, in schists : the structure of the 

 ground-mass also does not resemble that of schists ; nor do the rocks 

 themselves in this part of Charnwood Forest suggest very extensive 

 metamorphism. The idea, then, of a development in situ, as in the 

 case of many crystals of garnet, dipyr, hornblende, chiastolite, &c., 

 seems inadmissible. But if so, the aspect of the included minerals, 

 and the general structure of the rock, can only be explained on the 

 supposition that it is a tuff. The bands already mentioned, 

 which are undoubtedly fragmental, are certainly of volcanic origin., 

 The structure of the fragments in them and in the agglomerates of 

 Eatchet HiU and elsewhere is almost identical with the ground- 

 mass of these Sharpley rocks. Still, if the latter be of fragmental 



