SUMMARY AND CONCLUSIONS. 1235 



It is to be noted that the ores assigned above to the work of descending 

 waters alone do not include any sulphides. It is by no means asserted that 

 sulphide ores belonging to this subclass do not exist, but I know of no 

 sulphide deposit which can be certainly placed here. If more careful 

 investigation shall show that no important sulphide ores are deposited by 

 descending waters alone it will follow that all aqueous solution sulphide 

 ores belong either to the class deposited by ascending waters or to the class 

 produced by ascending and descending waters combined. It would 

 therefore follow that in the production of all sulphide ores ascending waters 

 are concerned. To my knowledge the only sulphide ores which are held 

 to be the result of descending waters alone are those of the Monte Cristo 

 district of Washington, described by Spurr." But Spurr's statement does 

 not seem to me to prove the conclusion. The mining has extended to only 

 a moderate depth in this district. So far as the facts are known, one might 

 explain the ores as being first concentrated by ascending waters and recon- 

 centrated by descending waters, or as produced by ascending waters 

 alone. It seems to me more probable that the interpretation should be 

 along the line applicable to so many other districts — a first concentration 

 of the sulphides by ascending waters and a later concentration by 

 descending waters. 



If the conclusion be established that ascending waters are concerned in 

 the production of all sulphide ores, to this extent the contention of 

 Posepny, who strongly insisted that all sulphide ores are the work of 

 ascending waters, is confirmed. His error would be that he overlooked 

 the importance of the concentrating effect of descending waters. Since 

 the tellurides are so closely associated with the sulphides it is highly 

 probable that they also will be found to be produced not by descending 

 waters alone, but by either ascending waters alone or by ascending and 

 descending waters combined. 



To the foregoing classification objections will at once occur. It may 

 be said that there are no sharp dividing lines between the divisions, classes, 

 and subclasses. But transitions are everywhere the law of nature. In a 

 previous chapter (see pp. 786-787, 904-905) I have explained that there 

 are gradations between different classes of rocks, and this statement 

 applies equally well to ore deposits. 



«Spurr, J. E., The ore deposits of Monte Cristo, Washington: Twenty-second Ann. Rept. U. S. 

 Geol. Survey, pt. 2, 1901, p. 857. 



