Dr. KiDD on the Mineralogy of St. David's, 83 



the mass is remarkably disposed to separate into flat rhomboidal 

 fragments, the surfaces of the laminse of which are sometimes inter- 

 spersed with a few small specks of white mica. 



Penherry, 



The rock constituting this summit, as may be satisfactorily ascer- 

 tained by insensibly graduating specimens, is of the same nature with 

 those already spoken of; though at first sight, and especially in par- 

 ticular parts, apparently very different. The hornblende gradu- 

 ally dsminishing in its proportion, or being intimately blended with 

 the substance of the felspar, often merely imparts an obscure shade 

 of green to the whole mass ; the presence of which colour princi- 

 pally assists the eye in recognizing the true nature of the rock ; and 

 but for which it might be confounded with a compact sandstone or 

 felspar. The same observation holds, but still more strongly, with 

 respect to the rock on which stands Roche Castle ; a ruin situated to 

 the north of the turnpike road, about half way between Haverford- 

 west and St. David's. This rock has, much more decidedly than 

 Penberry, the character of a compact sandstone : but in its geogra- 

 phical relation to the surrounding country, it exactly corresponds 

 with the preceding rocks, and with the numerous similar rocks of 

 the neighbourhood. However this may be, the surface of the 

 ground between Roche Castle and St. David's is scattered over with 

 numerous large boulders, as they might be called, very closely re- 

 sembling in their general character one or other of the three rock* 

 already described ; and all of them bearing strong marks of having 

 been the result of chemical formation. 



The rock of which Penberry is composed shews occasionally a 

 slight tendency to concentric disintegration j and the external part 



L 2 



