210 B. HILL AND T. G, BONNET ON THE 



being also of pyroclastic origin. Further, seeing that the ground- 

 mass is evidently felspathic, and apparently often to a large extent 

 consists of comminuted felspar, should we not expect that it would 

 be the first to lose its characteristic structure, and that it would 

 have to be quite melted before the larger fragments would be more 

 than slightly affected ? One does not of course forget the cases of 

 crystalline and even porphyritic structure in gneiss and many schists ; 

 but then the alteration even in the most highly altered of these 

 Charnwood rocks is far short of what has been undergone by the 

 latter. Hence in the great majority of these Charnwood rocks it 

 seems, on the whole, more probable that the larger, and even most 

 of the smaller, felspar crystals are of clastic, and in many of pyro- 

 clastic origin ; and so, by analogy, we incline, though more hesi- 

 tatingly, to the same origin for that in even the coarsely porphyritic 

 rocks of Peldar Tor and Bardon Hill. 



Next, with regard to the quartz grains. We may unhesitatingly 

 regard those of the grit of Steward's Hay, Bradgate-Stable quarry, 

 and Forest-Rock-Inn Spinney as of clastic origin. Following the same 

 method of investigation, we find that in igneous rocks (where the 

 quartz is not in crystals) the mineral is generally of a roundish 

 form, often seems to melt at its edge into the ground-mass, and 

 contains portions of the same. Now in the Peldar-Tor and the 

 Bardon rock the large size of the quartz grains, and the approach to 

 crystal shape, certainly favours the idea of their having formed in. 

 situ; they sometimes melt into the ground-mass, and occasionally 

 are pierced by, or even seem to contain small portions of it, espe- 

 cially the smaller granules. But then, just as with the felspar, wo 

 can proceed from the above grits, through such, examples as the 

 Forest-Gate, Bawdon-Castle, Broombriggs, and then the Monastery 

 and Benscliff rocks, to the Peldar-Tor and Bardon-Hill rocks. Also 

 we sometimes find subangular quartz fragments in true igneous 

 rocks, such as trachytes and some felsites ; and, on the other hand, 

 in the above grits there is more than once a distinct tendency to a 

 fusion of the quartz grains with the adjoining matrix*. Further, 

 we can hardly suppose that such large grains as are found in the 

 Peldar and Bardon rock could have been formed without complete 

 fusion and recrystallization of the finer ground-mass, and this does 

 not appear to have happened f. Here also, though with more hesi- 

 tation in the case of some of the smaller round grains, we consider 

 the quartz of clastic origin, in even the last-named instances. 

 The grains are extremely like those in the fragments of the breccias 

 of Hatchet Hill &c, though of smaller size, and like those in some 

 trachytic lavas. Thus they might be produced by the explosive 

 destruction of a quartz-trachyte. The leucite crystals of the Roman 



* In the Monastery rock, where the general original structure is well pre- 

 served, the, quartz grains may be paralleled now with those of the grits, now 

 with those of Peldar Tor. 



t There is not a trace of aggregate crystallization in these grains, which 

 seems unfavourable to the idea of their filling cavities. They might possibly be 

 pseudomorphs ; but of what ? 



