328 THEORIES OF ORE DISPOSITION HISTORICALLY CONSIDERED. 



its value. Indeed, for a time some of the most valuable deposits in 

 the West were entirely neglected by the prospector because they did 

 not possess the physical characteristics of the " true fissure vein,-' 

 This misconception arose from the fact that this, being the most 

 clearly defined form of deposit, had been the only one mentioned in 

 early si)eculations, and that hitherto the classification of text-books, 

 based as they were on the almost accidental characteristic of form, 

 relegated other types of deposit to a distinct and relatively subordi- 

 nate class, disregarding the fact that this class includes many of the 

 largest and most productive ore bodies, which may not only have the 

 same origin, but often be associated in the same deposit with a typical 

 fissure vein. 



Von Groddeck (on the other hand), who represents the most ad- 

 vanced scientific opinions of his time (1879), divides ore deposits into 

 two classes : 



1. Those formed contemporaneously with the inclosing rock, 

 whether {a) sedimentary or (6) eruptive. 



2. Those of latei- formation classed under two heads: 



(a) Those filling preexisting open spaces. 



(h) Metamorphic deposits formed by alteration of rock in 

 place. 

 His two main divisions corresponded to a certain extent with those 

 made in 1854 by J. D. Whitney (Metallic Wealth of the United 

 States), namely, stratified and unstratified. One dilTerence is that 

 metamorphic deposits were included by Whitney in the first division 

 and by Von Groddeck in his second. Neither recognized their true 

 importance, and the latter, while admitting that he included in this 

 class those that Stelzner had called metasomatic deposits, said they 

 could not be regarded as separate deposits, because they are only inci- 

 dental phenomena of the filling of cavities. 



As a means of obtaining a clear view of the whole field. Von Grod- 

 deck divided known deposits into types (54 in number), character- 

 ized in the main by their varying mineralogical and lithological asso- 

 ciations. Of these, 10 belong to his first subdivision, 5 to the second, 

 20 to the third, and 7 in part to the third and fourth, a classification 

 which he admitted nnjst be considered but tentative, owing to defects 

 in existing knowledge which could be remedied only w'hen all mines 

 could be studied on a monographic or exhaustive system. 



In America, though apparently uidnioAvn to Von Groddeck, such 

 monographic studies had already been made— that of the Comstock 

 lode by King (Fortieth Parallel reports, 1870), of the Lake Superior 

 copper deposits by Pumpelly (Michigan geological survey, 1873), 

 and that of the lead dei)osits of the Mississippi Valley by Chamberlin 

 (Wisconsin geological survey. 1873-1871)). These were followed in 

 the early eighties by reports on the Comstock lode by Becker, on Lead- 



