Correspondence — Mr. E» Wilson, 341 



the late Mr. D. Sharpe, and have myself more than once sug- 

 gested to geologists, but as yet, I fear, without much success, that 

 the laminar structure of the metamorphic schists is owing to the 

 same cause — gneiss being only a squeezed granite. 



G. POULETT SCROPE- 

 Fairlawn, Cobham, Surrey, June 5, 1868. 



ON FAULTS AND CONTOETIONS IN STRATA. 

 Sir, — I read with considerable interest a short paper in your May 

 number, by Mr. J. M. Wilson, attempting to explain the causes by 

 which contortions and faults are produced. Mr. Wilson's theory, 

 that " contortions are the inevitable result of the depression," and 

 " faults of the elevation of a curved surface," from its soundness and 

 simplicity is likely to be generally accepted ; at the same time I do 

 not think that all faults or contortions can be ascribed to the opera- 

 tion of one universal cause. In the first place, if such were the 

 case, should we, according to Mr. Wilson's view, ever find that the 

 direction of the fault hades (underlies) in the direction of the itpthrow? 

 Such cases do occur, though they are exceptional. Secondly, accord- 

 ing to Mr. Wilson's theory of faulting, the elevation of a very ex- 

 tensive area of the earth's surface is necessary for the production of 

 a complete series of upthrows and downthrows, as shown in Fig. 4, 

 p. 207, Geological Magazine. Now I have lately met with such 

 a series in a horizontal line, 136J feet long, in the Upper Eed Marls 

 of the Keuper Series, Nottingham. It occurs on the brow of the 

 hill near the Mapperley Eeservoir, and is well show^n in a road cut- 

 ting. I enclose a rough sketch of the section. I think there can be 

 no doubt that the cause w^hich produced that faulting acted locally, and 

 if that cause were the elevation of a curved surface (which perhaps 

 may have been the case), that curved surface was not due to the cur- 

 vature of the earth's surface, for over an horizontal area of 45J yards 

 there would be no appreciable curvature from such a source. If the 

 faults had all been vertical, or inclined in parallel directions, I should 

 have been inclined to adopt Sir C. Lyell's theory of cavities, but on a 

 smaller scale, such, for instance, as might be caused by the carrying 

 away, by percolating water, of salt, gypsum or other mineral in 

 chemical solution, or, under certain circumstances, in mechanical 

 suspension. The sinking of a stratum into a cavity could produce such 

 faulting as shown in Fig. 1. For the present case I would suggest 

 the following explanation in want of a better : — 





Ya- / - a ~ » \ \ 



■3'- ar~^ /-— ~:~_-^ _.\ \ \ 



F F F F 



Fig. 1 . Section of New Red Marls, Mapperley Road, Nottin2:ham. Average height of section, 5 feet 

 4 inches. Total length, 136 feet 6 inches. Greatest amount of faulting ascertainable, 2 feet 6 

 inches. L. L., Level of the Road. The strata on the right of section are obscured by dis- 

 tortion and exposure to the atmosphere. F F F lines of ifaulting. The letters a a, b b, c c, 

 indicaie the portions of the dislocated beds which were once continuous. 



