100 Ti-ansactions. 



The theory of lateral secretion received a new impulse from 

 the researches of Sandberger. It seemed competent to explain 

 the origin of many ore-veins, and, although strongly opposed 

 by Professor Stelzner of Freiburg and Professor Posepny of 

 Przibram, it found much support in America, in a more or less 

 modified form. 



Thus, Emmons,* discussing the manner in which he con- 

 siders the Leadville ore-deposits were produced, summarises 

 his views on ore-formation in general as follows : — 



(1.) Ore-deposits have been deposited from solution, rarely 

 in open cavities, most frequently by metasomatic 

 interchange. 



(2.) Solutions do not necessarily come directly upwards, 

 but simply follow the easiest channels of approach. 



(3.) The material was derived from sources within limited 

 and conceivable distance, very often the older intrusive 

 rocks. 

 Emmons, while supporting the principle of lateral secretion, dis- 

 claim.s the narrow views of Sandberger, who limits the source of 

 the vein-contents to the wall-rock in immediate contact with 

 the vein.f 



In the critical discussion which followed the publication of 

 Professor Posepny's paper on the genesis of ore-deposits, in 1893, 

 Blake and Winslow reaffirmed their belief that the zinc and lead 

 ores of Wisconsin were formed by lateral secretion. { 



Becker,§ while strongly dissenting from Posepny's view that 

 metasomatic replacement was incapable of producing such pro- 

 nounced ore-bodies as those at Leadville, makes a clear state- 

 ment of the supposed operation of metasomatic processes. He 

 says, " Eeplacement, like solution, must occur along fissures or 

 channels, and metasomatic ore-bodies will present analogies in 

 form to the open spaces of caves of solution." 



Rickardy discusses the problem of ore-formation from a wide 

 standpoint, and is not a dogmatic supporter of the extreme 

 doctrines of either ascension or lateral secretion. He affirms 

 that there is no ground for the belief in the existence of a reser- 

 voir of water at great depth, and maintains that all ascending 

 water must at one time have been descending water. 



This last can only be true in regard to meteoric waters. So 

 far as the existence of deep-seated water is concerned, his view 



* S. F. Emmons, " The Genesis of certain Ore-deposits," Trans. Am. 

 Inst. M.E., Vol. XX, p. 125. 



f " The Genesis of Ore-deposits," New York, 1901. ]). 199. 



X Loc. ciL, p. 188. 



§ Loc. cit, p. 206. 



II Loc. cit., pp. 190 and 211. 



