in reply to a Paper by Mr. E. W. Brayley, jun. 105 



the contrary, as my correspondent before quoted observes, 

 " the basins are not only often of very regular figure, but are 

 cut in the hardest rocks, where no other derangement of the 

 surface is visible. And they are also very distinguishable from 

 the hollows worn in the softer parts of some rocks by the 

 effects of weather." These cavities are not only, as Dr. Mac- 

 Culloch states, occasionally circular in their boundary, and 

 as regularly spheroidal internally as if they had been shaped 

 in a turning lathe, but their sides also are smooth and even ; 

 and these circumstances appear to me to be decisive of the 

 question. Dr. MacCulloch, it is true, ascribes this regularity 

 of form to " the uniform texture of the granite," Now the 

 constituent parts of the granite which most generally prevails 

 in Devonshire, are stated to be quartz, felspar and mica; and 

 we are told that these several materials are of different de- 

 grees of hardness. Mr. Brayley has spoken of " the felspar of 

 the base as dull, earthy and decomposing" ("Devon," p. 251), 

 and of another ofthedecomponent parts as "almost indestruc- 

 tible." This being the case, then, I maintain that the decom- 

 position, which is admitted to be going on at present as here- 

 tofore, would necessarily follow the softer particles of the rock ; 

 and the consequence would be, that the figure of the cavities 

 in question would become, in all cases, irregular, and bear 

 little or no resemblance to the rock-basins as they now are, 

 and as Dr. MacCulloch describes them. And not only would 

 they be irregular in their form, but the surface of these ca- 

 vities would also be rough and crumbly, the " soft, earthy 

 part having decayed," and left the " indestructible" portions 

 projecting. But this is not the fact ; and Mr. Brayley has ac- 

 cordingly admitted (" Devon," p. 290) that in his examinations 

 of the rock-basins on the summit of Carnbrea Hill, near Red- 

 ruth in Cornwall, " he did not find the sides of the basins 

 crumbly." The inference appears to me to be obvious and 

 conclusive: the sides of the basins ought to be rough and 

 crumbly, if formed as Dr. MacCulloch represents, and if the 

 constituent parts of granite, as is also affirmed, are of different 

 degrees of hardness or durability ; but they are not rough and 

 crumbly, and therefore not formed by the only natural pro- 

 cess to which their formation is attributed. 



What Mr. Brayley however considers as the strongest evi- 

 dence of the artificial origin of these cavities, but which, not- 

 withstanding, has escaped Dr. MacCulloch's notice, is as fol- 

 lows : " Many of the rock-basins on Carnbrea are crossed 

 by veins of porphyry or porphyritic granite, which traverse 

 the earns, and which, offering a much greater resistance to 

 the action of decomposing agents than the granite itself, have 



N.S. Vol. 9, No. 50. Feb. 1831, P been 



