Geological Society. 387 



ject to disturbing agents similar to tl-.ose which exposed the district 

 under review. 



Lastly. With respect to the agents which have modified the surface 

 of Coalbrook Dale, the author is of opinion that it was denuded, in 

 part, while beneath the level of the ocean ; that the lower bed of de- 

 tritus, containing angular gravel and large masses of coal, proves a 

 sudden and short cataclysm ; while the upper beds of rounded gravel, 

 containing recent shells, indicate the long-continued action of a body 

 of water, since the existence of the present Testacea of our coasts. 



A letter from R. W. Fox, Esq., addressed to Sir Charles Lemon, 

 Bart., M.P., F.G.S., " On the Formation of Mineral Veins," was 

 then read. 



Mr. Fox is of opinion that mineral veins were originally fissures 

 probably caused by changes in the earth's temperature; that they 

 were small at first and gradually increased in their dimensions ; and 

 that the mineral contents progressively accumulated during the whole 

 period of the development of the fissures ; and as changes in the earth's 

 temperature might produce changes in the direction and intensity of 

 the terrestrial magnetic curves, he conceives that electricity may have 

 powerfully influenced the existing arrangement of the contents of these 

 fissures. 



Copper, tin, iron, and zinc, in combination with sulphuric and 

 muriatic acids, being very soluble in water, Mr. Fox says, they 

 would in this state be capable of conducting voltaic electricity ; and 

 as the rocks forming the walls of the veins contain different salts, 

 they would be in opposite electrical conditions, and hence currents 

 would be generated and readily transmitted through the fissures, 

 and in time the metals would be separated from their solvents and 

 deposited in the veins. But, on the known principles of electro- 

 magnetism, Mr. Fox adds, it is evident that such currents would be 

 more or less influenced by the magnetism of the earth ; and there- 

 fore that they would not pass from north to south or from south to 

 north as easily as from east to west, but more so than from west to 

 east. 



The author then offers some observations relative to the production 

 of sulphurets from the decomposition of the metallic sulphates ; and 

 explains how fissures, gradually widening, would be successively filled, 

 and would account for veins occurring within veins ; he offers some 

 remarks also on the greater productiveness exhibited at the points 

 where veins pass from one formation to another, and is of opinion 

 that the fact may be explained by supposing the rock in which the 

 vein is productive to have been electro- negative. 



In conclusion Mr. Fox states, that if in other parts of the world 

 veins may be found to deviate from an east and west direction much 

 more than they do in England, the apparent discrepancy may be ex- 

 plained by the rocks having yielded more easily in one direction than 

 in another, and from a difference in the direction of the magnetic me- 

 ridian in different countries, as well as from the probability that it has 

 v/»ried greatly at different ejjochs. 



2 Z2 



