PrwECARBOlS'IFEROUS EOCKS OP CHARNWOOD FOREST. 345 



origin, it may fairly be asked, 'WTiat has become of the lapilli ? 

 why are they not as usual more or less clearly defined in the slide ? 

 To this we may reply, that here and there we do meet with faint indi- 

 cations of these ; that in two intercalated bands separated by no clear 

 line of division they unquestionably occur ; that a similar tendency 

 to disappear may be occasionally noticed in slides from rocks in 

 other parts of Charnwood which are of undoubtedly clastic origin ; 

 and, lastly, that in some comparatively modern tuffs a similar ob- 

 literation of the fragments may be witnessed *. 



We suppose, then, that this rock of High Sharpley and elsewhere 

 was once a rather fine uniform rhyolitic tufi", consisting of lapilli 

 and volcanic dust, mixed with quartz and felspar crystals, which per- 

 haps no long time after deposition was exposed to the action of per- 

 colating water or vapour, and, as it were, partly rotted t, but without 

 destroying the included felspar crystals. It was then consolidated, 

 cleaved, and gradually brought to its present condition. The rock 

 of High Sharpley much resembles some of the " porphyroides " of the 

 Ardennes, the chief difference being that sericite is much less con- 

 spicuously present in the former than in the latter J. 



AYe described in Part II. the ordinary rock of Peldar Tor. Since 

 then we have had additional sections prepared. The study of these 

 and our field-work confirm us in the opinion, there expressed, that 

 the rock is of clastic origin. We may, however, remark that the 

 quartz and felspar crystals are in most respects identical with those 

 of Sharpley ; and the general character of the ground-mass, especially 

 with crossed Nicols, is the same. As the rock in the main mass of 

 Eatchet Hill§ is indubitably pyroclastic, and is now proved by super- 

 position on the typical Sharpley rock to be equivalent to that of 

 Peldar Tor, our view as to the nature of the latter and of Sharpley 

 receives additional confirmation §. :' 



The rock near Copt-Oak church (noticed vol. xxxiii. p. 771) has 



* As, for example, in a white tuff from Monte Venda/Euganean Hills, of the 

 British-Museum collection, for a sight of which we are indebted to Mr. T. Davie?, 

 r.Gr.S. Since writing the above, we find a somewliat similar case described 

 by Prof. Geikie, " Volcanic rocks of Firth of Forth," Tr. R. S. Edin. vol. xxix. 

 p. 474. 



t Lapilli are very commonly outhned by a black margin, which probably 

 largely owes its colour to ferric oxides. The passage of water or vapour through 

 the mass would decompose the iron oxide (forming carbonates, &c.), and thu3 

 obscure the structure. 



J I am indebted to Prof. Eenard for specimens of porphyroides from 

 Laifour and Mairus (described in the well-known memoir ' Les Eoches Plut. de la 

 Belgique ' &c.). Early in the present year, I fortunately had the opportunity 

 of showing him my collection of rocks and slides from Charnwood. He in- 

 formed me that the resemblance of the Sharpley, Peldar, and Bardon-Hill rocks 

 to those of the Ardennes was most remarkable, and expressed a distinct opinion 

 that none of them were lavas. In the above memoir it is suggested that the 

 quartz and felspar crystals have been developed in situ ; but after examination 

 of my collection, he stated that, in the case of Charnwood, he thought the 

 view mentioned above worthy of serious consideration. — T. G. B. 



§ A careful search over the rocky ridge will show here and there near the 

 base a tendency to recur to the Sharpley type, and liigher up bands closely 

 approachmg the Peldar-Tor type. 



