48 Analyses of Books, [Jult^ 



tained in the granite of this district is shorL This occurs in 

 great plenty. In one spot, on the coast near Cape Cornwall, of 

 several hundred yards in extent, this mineral forms so consider- 

 able a proportion of the rock, as to give it quite a new aspect, 

 and has indeed procured it from geologists a distinct appellation, 

 viz. short-rock ..... .The locality now mentioned, and the cele- 

 brated Roach Rock, in the neighbourhood of Bodmin, are the 

 only places in Cornwall where 1 have heard of this modification 

 of granite being found in mass. In the form of veins, indeed, 

 traversing both the granite and slate at their junction, it is very 

 common." 



The slate formation, ** is much more complicated than the 

 last, and affords much greater scope for geological research. It 

 comprehends, as far as I have been able to ascertain^ five distinct 

 rocks. These are clayslate, hornblende rock, greenstone, com- 

 pact felspar, and slaty felspar By felspar rock, I mean a 



rock of small granular structure, consisting, apparently, princi- 

 pally, or almost wholly, of felspar. By slaty felspar, I mean a 

 rock apparently of the same composition, or only with the addi- 

 tion of a very small portion of mica, with a distinct slaty frac- 

 ture. These five rocks, constituting the assemblage to which I 

 have given the name of the slate formation, occur in beds of 

 various magnitude, alternating with each other ; but with one 

 very small exception, I have uniformly found the slaty felspar 

 rock in immediate contact with the granite ; and I think it not 

 improbable that in proportion as we recede from this central 

 rock, we shall find the slaty felspar become less frequent, and 

 be finally superseded by some of the varieties of clayslate." . . . . 

 *' The rock which I have named compact felspar, which consists 

 principally, I believe, of compact felspar with a little quartz, I 

 have so named in deference to my excellent and learned friend 

 Prof. Jameson : it may, however, be considered as a variety of 

 greenstone. The only difference between it and common green- 

 stone, is its containing a more minute portion of hornblende, and 

 being, consequently, of a Hghter colour than that rock generally 



is.** The author has presented to the Society specimens of 



every rock which he has described. 



XIII. An Account of the Alluvial Depositions at Sandrj/cock. 

 ]By the late Philip Rashleigh, Esq.* 



The alluvial beds described in this communication are very 

 similar to those at the stream-work of Poth, of which an account 

 was long since given by Mr. Rashleigh, at the end of his work 

 entitled " Specimens of British Minerals." 



XIV. Observations on the Alluvial Strata at Poth, Sandrucock, 

 mtd Pentuan. By John Hawkins, Esq. FRS. &c. Hon. Mem. 

 GSC. 



These observations will not admit of profitable abridgment. 



• Prawn up in 179?, and communicated by Jolm Hawkins, Esq. Sept. 1819. 



