256 Rev, Mr. Conj/beare on the [April, 



be the variety of substances contained in its brecciated form. 

 Deluc has mentioned two only of these, the Hmestone and grey- 

 "wacke, though he insinuates that there are others, and appears 

 (if I rightly understand the paragraph) to apprehend that of these 

 the limestone only can be traced to any neighbouring rock, an 

 opinion which, in its full extent, seems untenable. The following 

 catalogue presents a tolerably faithful description of the frag- 

 ments occurring in the breccia of Dawlish and Teignmouth, with 

 the addition of some few from other quarters. 



Granite and Porphi/ritic Rocks. — These form a very consider- 

 able portion of the imbedded fragments. A'. A minute aggrega- 

 tion of pale reddish-brown crystalline felspar, quartz, and common 

 schorl. A'^ Same with felspar, somewhat darker, and more 

 crystalline. A\ Same mixture, with lighter-coloured felspar, and 

 the schorl distributed in small contemporaneous veins, as well as 

 intermixed in the mass. B. Felspar same as A nodules of 

 quartz, and minute portions, apparently crystalline, of chlorit? 

 Structure semiporphyritic. C. Minute aggregate of earthy fel- 

 spar, of a pale dirty-red, quartz, and chlorit. C-. Same with the 

 felspar, less earthy, and of a deeper red. D. Porphyritic base, 

 of a purplish-white, apparently a minute aggregation of earthy 

 felspar and quartz, imbedded quartz in small nodules, and some 

 crystalline felspar (semivitreous). D-. The same with the quartz 

 so much predominant in its base as to give it, at first sight, the 

 aspect of a sandstone, or greywacke.* D^. Same with imbed- 

 ded semivitreous felspar, and common felspar in various stages 

 of decomposition (from the bed of the river Exe). D''. Base 

 more felspathic, and of a deeper purple, much disintegrated, 

 with the exception of the semivitreous felspar. Many cavities 

 filled with earthy felspar. D\ Porphyry, base compact felspar, 

 of a greyish-white, having imbedded small nodules of quartz, 

 and penetrated by numerous cavities, apparently left by the dis- 

 integration of crystals of felspar, and the loss of the powdery 

 matter so produced. (This remarkable character I have 

 observed in more than one porphyry from Cornwall.) E. Base, 

 a minute aggregation of earthy felspar, quartz, and chlorit, 

 coloured green by the latter, imbedded minute crystals of flesh- 

 coloured felspar, and small nodules of quartz. (Descent of 

 Haldon on the eastern side.) All these occur in various stages 

 of disintegration. Those prophyries approaching the nearest in 

 colour to the marie which surrounds them are, when far advanced 

 in this state, not readily distinguishable from that substance, the 

 outline of the original fragment being so broken down and lost, 

 that it appears to pass insensibly into the imbedding mass. 

 Hence, perhaps, som egeologists, of no inconsiderable authority, 

 have been induced to suspect that these, and, by consequence, 



• It is distinguishable, however, by its fusing readily before the blow-pipe into a 

 vitreous glolnile. On breaking too the laigcr masses, the interior is found to be some- 

 what more felspathic 



