412 THEORIES OF METALLIC VEINS. 



injected from below, in a state of igneous fusion. A third 

 hypothesis has been recently proposed, which refers the 

 filling of veins to a process of Sublimation from subjacent 

 )nasses of intensely heated mineral matter, into apertures 

 and fissures of the superincumbent Rocks.* A fourth hy- 

 pothesis considers veins to have been slowly filled by Segre- 

 gation, or infiltration ; sometimes into contemporaneous 

 cracks and cavities, formed during the contraction and 

 consolidation of the originally soft substances of the rocks 

 tiiemselves ; and more frequently into fissures produced by 

 the fracture and dislocation of the solid strata. Segregation 

 of this kind may have taken place from electro-chemical 

 agency, continued during long periods of time.f 



* In the London and Edin. Phil. Mag. March, 1829, p. 172, Mr. Patterson 

 lias publislied the result of his experiments in making artificial Lead Ore 

 (Galena) is an Earthen tube, highly heated in the middle. After causing 

 the steam of water to pass over a quantity of Galena, placed in the hottest 

 portion of this tube, the water was decomposed, and all the Galena had been 

 sublimed from the heated part and deposited again in colder parts of the tube, 

 in cubes which exactly resembled the original Ore. No pure Lead was 

 formed. From this deposition of Galena, in a highly crystalline form, from 

 its vapour in contact with steam, he draws the important conclusion, that 

 Galena might, in some instances, have been supplied to mineral veins by 

 sublimation from below. 



Dr. Daubeny has found by a recent experiment that if steam be passed 

 througli heated Boracic Acid, it takes up and carries along with it a portion 

 of the Acid, which per se does not sublime. This experiment illustrates the 

 sublimation of Boracic Acid in volcanic craters. 



t The observations of Mr. Fox on the electro-magnetic properties of 

 metalliferous veins in Cornwall, (Phil. Trans. 1830, &c.) seem to throw 

 new light upon this obscure and difficult subject. And the experiments of 

 M. Becquerel on the artificial production of crystallized insoluble compounds 

 of Copper, Lead, Lime, &,c. by the slow and long continued reaction 

 and transportation of the elements of soluble compounds, (see Becquerel, 

 Traile de I'Electricite, T, i. e, 7, page 547, 1834,) appear to explain many 

 chemical changes that may have taken place under the influence of feeble 

 electrical currents in the interior of the earth, and more especially in 

 Veins, 



I have been favoured by Professor Wheatstone with the following brief 

 explanation of the experiments here quoted. 



•' When two bodies, one of which is liquid, react very feebly on each 



