770 C. R. VAN HISE 



and exploitation ? By these criteria I am willing that the clas- 

 sification shall be tested. 



As an illustration of the practical usefulness of the classifica- 

 tion is the connection between genesis and depth. The character 

 of a deposit in most cases will determine to which class it belongs. 

 Where the ores are deposited by ascending waters alone it has 

 been pointed out that this is favorable to their continuity to great 

 depth. Therefore, where a given ore deposit has been shown to 

 belong to this class, the expenditure of money for deep explora- 

 tion may be warranted, although, as already pointed out, p. 757, 

 such deposits may decrease in richness with depth. Where a 

 deposit is produced by descending waters alone, the probable 

 extent in depth is much more limited. In such cases, when the 

 bottom of the rich product is reached, it would be the height of 

 folly to expend money in deep exploration. Where the ore 

 deposit belongs to the third class, that produced by ascending 

 and descending waters combined, there will, again, be a richer 

 upper belt composed of rich oxidized and sulphureted deposits 

 which we cannot hope will be duplicated at depth. To illustrate : 

 it would be very foolish, at Ducktown, Tenn., to sink a drill hole 

 or shaft into the lean cupriferous pyrrhotite with the hope of find- 

 ing rich sulphurets such as those which were mined near the 

 level of groundwater. Those who have spent money in deep 

 prospecting of the lean pyrrhotite in the Appalachian range will 

 doubtless agree to this statement. Deposits produced by two 

 concentrations may grade into the class produced by ascending 

 water alone, and after the transition the deposit may be rich 

 enough to warrant exploitation at depth ; but if such work be 

 undertaken it must be done with the understanding that the rich 

 upper products will not be reduplicated at depth. It therefore 

 appears to me that the determination to which of the classes 

 of ore deposits produced by underground waters a given ore 

 deposit belongs has a direct and very important practical bearing 

 upon its exploration and exploitation. 



C. R. Van Hise. 



