EXPLANATION OF PLATE 68. 109 



Plate 68. V. I. p. 420. 



Section showing the basin-shaped disposition of Strata 

 belonging to the Tertiary and Cretaceous Formations, in 

 the Basin of London, and illustrating the causes of the 

 rise of water in Artesian Wells. See V. I. p. 421. Note. 

 (Original.) 



servable in them 1 Copper, Tin, Iron, and Zinc, in combination with 

 the sulphuric 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 dif- 

 ferent salts would undoubtedly become in different or opposite electri- 

 cal conditions ; and hence, if there were no other cause, electric cur- 

 rents would be generated, and be readily transmitted through the 

 fissurestontaining water with salts in solution ; and decompositions of 

 the salts and a transference of their elements, in some cases, to great 

 distances, would be the natural result. But, on the known principles 

 of Electro-magnetism, it is evident chat 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 frorn^ W. to E. The 

 terrestrial magnetism would therefore tend, in a greater or less degree, 

 to direct the voltaic currents through those fissures which might ap- 

 proximate to an east and west bearing, and in separating the saline 

 constituents, would deposite the metal' within or near the electro-nega- 

 tive rock, and the acid would be determined towards the electro-posi- 

 tive 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 oxygen 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 oxides found in our mines. The con- 

 tinued circulation of the waters would, in time, bring most of the solu- 

 ble salts under the influence of these currents, till the metals were in 

 great measure separated from the solvents, and deposited in the East 

 VOL. II. 10 



