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THE GEOLOGIST. 



would acquire a crystalliue nature. Thus some of the ingredients found as 

 components of granite and other igneous rocks would be developed. This 

 may be supposed to be the effect of lieat, which would affect what would 

 otherwise be ordinarily stratified rocks. I consider that this hypothesis is 

 much strengthened by the fact (assuming, as from the nature of granite I think 

 I may, that this geological doctrine is a fact) that these rocks underlie those 

 properly stratified and fossiliferous. The metamorphic rocks appear to be 

 ordinary stratified rocks subjected to the influence of heat. The hypothesis 

 alluded to, if accepted as true, or even probable, explains their position. The 

 heat of the igneous rocks would not reach those purely sedimentary, but only 

 alter rocks with which they were directly connected. If it be said, as it has 

 been, that some metamorphic rocks do not exhibit the influence of heat, I ad- 

 vise that the objectors consider the effect of age upon any deposit ; and also 

 the way, tlie possible way, in which this phenomenon can be accounted for, if 

 they can discover any, and reject this explanation. I do not see what other 

 explanatory hypothesis can be found. — I. A. Davies, — How sedimentary mat- 

 ter or any precipitate could be derived from higlily heated basement-rock, as 

 Lardner's hypothesis requires, it is difiicult to conceive. As altered sedi- 

 mentary matter (sand, clay, and limestone)' the materials of the metamorphic 

 rocks might plainly have come from the waste of the first uprising lands. 



The position of the metamorphic rocks in relation both with the igneous rocks 

 and unaltered sedimentary rocks affords incontrovertible evidence of their 

 having been usual sediments altered and distorted by heat. 



Suggestion respecting Rock-basins. — Sm, — Whilst reading in your 

 periodical for August the interesting article by Mr. Rupert Jones on the 

 weathering of granite, a conjecture presented itseK to me as to the pro- 

 bable cause of the primary basins on some of the surfaces of the granite. It is 

 this — whether the basins, if they correspond with distinct masses of rock, may 

 not be produced by the shrinking of compressed cooling masses. I might add 

 in illustration, I conceived that a like process might occasion the concave and 

 convex jomts in the basaltic pillars at the Giant's Causeway. This is merely 

 a suggestion, which may or may not be tenable ; if it be, you are quite at 

 liberty to publish it should you think fit. — Yours respectfully, George Renning, 

 Sheffield. — Our correspondent will see iii Mr. Rupert Jones' paper, at pages 

 307 and 308, that the effects of contraction in cooling have not escaped observa- 

 tion ; and he will further see, at page 311, that Mr. Ormerod recognizes the 

 horizontal planes of fracture or fissurage as probably Hmiting the depth of at 

 least some of the basins. We may take this occasion, in reference to the re- 

 marks of our correspondent, Mr. Drake, in our September number, on the artificial 

 origin of rock-basins, to express our regret that Mr. Rupert Jones did not refer 

 to that interesting aspect of the subject; probably he wished that readers 

 should refer on this point to Mr. Omerod's valuable memoir from which he 

 largely quoted, and in wliich will be found some observations on the circular 

 cavities in boulder-blocks in stream-courses, to which class of basins Mr. Drake 

 refers in the latter part of his communication. 



Localities for Mammalian Remains. — Bones of elephant, rliinoceros, 

 and ox from the gravel, at Brockhall, Lawford, were presented to the Geological 

 Society, in 1833, by the Rev. Wm. Thornton. Shells, and bones of mammalia, 

 from Stuttoii, Suffolk, were also presented by Mr. Edw. Charlesworth in 1835. 

 — P.G.S., London. 



