EXPLANATION OF PLATE 68. 109 



Plate 68. V. I. p. 563. 



Section shewing the basin-shaped disposition of Strata 

 belonging to the Tertiary and Cretaceous Formations, in 

 the Basin of London, and illustrating the causes of the 

 rrse of water in Artesian Wells. See V. I. p. 564. Note. 

 (Original.) 



servable in them? Copper, Tin, Iron, and Zinc, in combination 

 with the sulplmric and muriatic acids, being very soluble in water, 

 are, in this state, capable of conducting voltaic electricity ; so, if by 

 means of infiltration, or any other process, we suppose the water 

 to have been impregnated with any of these metallic salts, the 

 rocks containing different salts would undoubtedly become in diffe- 

 rent or opposite electrical conditions ; and hence, if there were no 

 other cause, electric currents would be generated, and be readily 

 transmitted through the fissures containing water with salts in solu- 

 tion ; and decompositions of the salts and a transference of their 

 elements, in some cases, to great distances, would be the natural re- 

 sult. But, on the known principles of Electro-magnetism , it is evi- 

 dent that such currents would be more or less influenced in their 

 direction and intensity by the magnetism of the earth. They cannot, 

 for instance, pass from N. to S. or from S. to N. so easily as from 

 E. to W. but more so than from W. to E. The terrestrial magne- 

 tism would therefore tend, in a greater or less degree, to direct the 

 voltaic currents through those fissures which might approximate to 

 an east and west bearing, and in separating the saline constituents, 

 would deposit the metal within or near the electro-negative rock, 

 and the acid would be determined towards the electro-positive rock, 

 and probably enter new combinations. Or, the sulphuric acid might, 

 by means of the same agency, be resolved into its elements ; in which 

 case the sulphur would take the direction of the metal, and the ox- 

 ygen of the acid, and in this way, the metallic sulphurets may have 

 probably their origin ; for, if I mistake not, the metallic sulphates^ 

 supposing them to have been the prevailing salts, as at present, 

 would be fully adequate to supply all the sulphur required by the 

 same metals to form sulphurets ; indeed more than sufficient, if we 

 deduct the oxide of tin, and other metalliferous oxydes found in our 

 mines. The continued circulation of the waters would, in time, 

 bring most of the soluble salts under the influence of these currents, 

 till the metals were in great measure separated from their solvents, 



