in reply to a Paper by Mr. E. W. Brayley, jun. 107 



Mr. Brayley is of opinion that Dr. MacCulloch has rendered 

 in the highest degree probable. To me however, I must take 

 the liberty of saying, the proofs adduced are not by any means 

 so satisfactory as Mr. Brayley supposes them to be. Some 

 kinds of rocks, and even some rare specimens of particular sorts 

 of granite, may be unquestionably spheroidal; but to infer 

 hence that all granite is so, would surely be much too hasty, 

 and can scarcely be satisfactory even to those who have a fa- 

 vourite notion to support. But that the structure of the De- 

 vonshire granite is not of this kind appears evident from the 

 following considerations. In the first place, if it were so, this 

 ought to be apparent on inspecting it. The crystals, for in- 

 stance, are usually large and very distinct ; but have they any 

 appearance of a concentric or spherical arrangement ? Cer- 

 tainly not: they seem to be thrown together in confusion, 

 and have in general no regular arrangement whatever. 



Again, the direction of the fissures in this granite are clearly 

 adverse to the supposition of its spheroidal construction. 

 Masses of this rock are divided into cuboidal or laminar 

 blocks, bounded by fissures horizontal, perpendicular, or in- 

 clined, often " mere mathematical planes and preserving an 

 exact parallelism among themselves ;" whereas, if the consti- 

 tuent parts of the granite had a spherical arrangement, these 

 blocks surely ought to be spheroids, and the fissures of a cir- 

 cular form. They would separate like the coats of an onion, 

 " whether the fissures, as originally existing in the granite, 

 are to be considered as the effects of contraction produced in 

 the mass by the evaporation of water, or by the abstraction of 

 heat." Much is said, it is true, about the boulders of this 

 rock, and the rounded form of the edges and corners of the 

 blocks and the laminae. To this it may be replied, that all the 

 projections of the granite, the corners, and the edges, are most 

 worn because they are most exposed to the action of the at- 

 mosphere, to which their decomposition is attributed, and that 

 this would be the case, whether there were anything spherical 

 in the arrangement of their constituent parts, or not ; so that 

 no argument in favour of such arrangement can be derived 

 from this circumstance, of sufficient weight to decide the ques- 

 tion. Proof therefore being wanting of the spheroidal structure 

 of this granite, all reasoning from it in favour of the forma- 

 tion of rock-basins by a natural process, falls to the ground*. 



On 



* Mr. Brayley has mentioned the Logan on the Teign in connection 

 with this subject, and has taken it for granted that its form is spheroidal. 

 But his account of it is in the main particulars erroneous. Having taken 

 a slight sketch of it myself, on the spot, I can speak of it without hesitation. 

 It is not properly seated, as he observes, " in the channel of the river," but 



P2 at 



