LAMINATION OF CLAY. 227 



of the origin of mineral veins,, it can be experimentally 

 shown that a schistose structure may be given to clays 

 and sandstone by voltaic action.* 



There is often a very remarkable regularity in the 

 direction of mineral veins: throughout Cornwall,, for 

 instance, they most commonly have a bearing from the 

 E. of N. to the W. of S. It has hence been inferred 

 that they observe some relation to the magnetic poles of 

 the earth. However this may be, it is certain that the 

 ore in any lodes which are in a direction at right angles, 

 or nearly so, to this main line, differs in character from 

 that found in these, so called, east and west lobes. f 



The sources of chemical action in the earth are nume- 

 rous. Water percolating through the soil, and finding 

 its way to great depths through fissures in the rocks, 

 carries with it oxygen and various salts in solution. 

 Water again rising from below, whether infiltrated from 

 the ocean or derived from other sources, is usually of a 

 high temperature, and it always contains a large quan- 

 tity of saline matter. J By these causes alone chemical 



* See Becquerel, Traite Experimental de TElectricite, fyc. Elec- 

 trical Experiments on the formation of Artificial Crystals : by 

 Andrew Crosse, Esq. ; ] British Association Reports, vol. v., 183G. 

 The lamination of clay and other substances is described in rny 

 memoir referred to, Note p. 226. 



f Report on the Geology of Cornwall, Devon, and "West Somer- 

 set, by Sir Henry T. De la Beche : Theoretical observations on the 

 formation and filing of Mineral Veins and Common Faults, p. 349. 



I The following analyses of waters from deep mines were made 

 by me in 1840, and, with many others, published in the Reports of 

 the Royal Cornwall Polytechnic Society. 

 Consolidated Mines, Gwennap, 



Cornwall. In 1,000 grains of water. 



Muriate of soda . .1*5 



Sulphate of lime . 

 Sulphate of iron . 

 Sulphate of copper 

 Silica . 

 Alumina 



Total 



5 

 15 

 1-25 

 15 

 3- 



