350 ORIGIN AND DKVELOPMENT OF ORE-DEPOSITS. 



Sec. 11. — Theories af Mineral Deposition with reference to Lode 



phenomena. 



The formation of our fissure-lodes (vein deposits, fissure 

 fillings and capels) throws very much light on the origin of 

 ore-deposits generally, and — thanks to the labours of a host of 

 careful observers, among whom our former colleagues, W. Jory 

 Henwood, Warington Smyth, and C. Le Neve Foster, deserve 

 special mention — the leading phenomena of our lodes are very 

 well known. It is generally admitted that the lodes themselves 

 have originated either in actual fissures or in enlarged joints ; 

 that the lode-fillings are sometimes mechanical, but more usually 

 chemical ; that the mechanical filling was mainly derived from 

 the sides (though perhaps in rare instances partly from the 

 surface) ; that the chemical filling has always been effected by 

 infiltrating and circulating solutions ; and that it has taken place 

 at various times, yet usually with a definite order of succession. 

 Having already given (Sec. 4) specific examples of several 

 lodes, and of the characteristic phenomena of lodes in general 

 in the West of England, we may now proceed to consider the 

 more important theories of mineral deposits which have been 

 adopted by various writers and at different times. 



Confining the enquiry for the present to fissure-lodes, and 

 to the metalliferous minerals, capels, and vein-stones occurring 

 therein with which we are familiar in the west, we have to 

 consider the following theories :* 



a. — That the fissures have been filled hy injection. So far as 

 lodes proper are concerned, this theory may be at once 

 dismissed, though it was formerly held as an axiom by 

 many followers of Hutton, (not I think by Hutton 

 himself) who were impressed by the phenomena of 

 injected dikes, but who had little or no acquaintance 

 with lode-phenomona. There are very few now who 

 believe that metallic ores and veinstones have been 

 injected into open fissures,! yet in another and more 



* The history of opinion on this subject of the genesis of mineral veins has 

 been very well dealt with by Mr. J. A. Phillips in his work on Ore-deposits, pub. 

 in 1884, p.p. 73-100. 



f There are still some geological writers, however, who still maintain the 

 igneous origin even of masses of vein quartz. See Sterry Hunt, Mineral 

 Physiography, p. 94 et seq. 



