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LXXI. Reply to Dr. Boase's " Remarks on Mr. Hopkins's 

 * Researches i7i Physical Geology' " in the 'Number for July. 

 By W. Hopkins, £5^., M.A., F.G.S., of St. Peter's College, 

 Cambridge, 



[Continued from p. 175, and concluded.] 



TPHE two theories of the formation of veins of which I 

 "*■ have spoken, equally depend on some process of infiltra- 

 tion or segregation into previously existing fissures, and differ 

 only in the manner in which those fissures are supposed to 

 have been formed, in the one case by dislocation, in the other 

 by the mass becoming jointed. There is no reason why both 

 should not be true as applied not merely to veins of different 

 districts, but also to different veins of the same district, and 

 both will enable us to account for nearly all the phaenomena 

 referrible to mechanical causes which veins present to us. 

 Let us now proceed to analyse the rival theory of the con- 

 temporaneous formation of veins, of which Dr. Boase has 

 been one of the ablest advocates. 



In the first place, then. What are the physical causes 

 which this theory assigns for the observed phaenomena? We 

 cannot of course do better than answer this question by a 

 quotation from Dr. Boase's " Primary Geology *." " Is it 

 not within the bounds of probability that the chemical union 

 of the elements of the fused mass (of the earth's crust) whence 

 resulted such a vast body of definite minerals, should be ac- 

 companied by the evolution of numerous currents of electri- 

 city, or of analogous fluids ? for we know that the oscillations 

 of the particles of matter, whether produced mechanically or 

 during chemical combinations, will elicit streams both of 

 common and galvanic electricity. If, then, it be acceded 

 that the primary rocks may have been traversed by such cur- 

 rents during their formation, we have an explanation of the 

 regular disposition of the granitic rocks, of veins, and other 

 crystalline substances ; and indeed not only of the subordinate 

 parts but of the entire mass. 



" This idea will remind the reader of Mr. R.W. Fox's ex- 

 periments, from which he has concluded that the Cornish me- 

 talliferous veins were formed by electro-magnetism. By such 

 imaginary currents, crossing each other in different directions, 

 we also fancy that the phaenomena of intersecting veins might 

 be accounted for, the more powerful ones having uninter- 

 ruptedly continued their course, whilst the weaker ones ex- 



* p. 385. 



