NOVEMBEK 22, 1901.] 



SCIENCE. 



793 



depth, as shown by the Lake Superior iron 

 mines. And where the topographic forms 

 are those of great and sharp relief, there 

 the descending waters go to very great 

 depths. In the San Juan region, for in- 

 stance, are wonderfully steep slopes and 

 very great canyons. Here the water de- 

 scends a long way on its downward course 

 before it turns laterally and upward on its 

 way to the valleys. I have visited the San 

 Juan region during the past week with 

 other geologists, and in some cases we saw 

 the effect of descending water to a depth of 

 3,000 feet below the surface. It has already 

 been explained that in the early history of 

 this region the conditions were ideal for a 

 first precipitation of ores by ascending wa- 

 ters. They are now no less ideal for a re- 

 concentration by descending waters. 



If the classification advocated be based 

 upon facts, it gives valuable criteria to 

 mining men for the exploration and exploit- 

 ation of their mines. Many millions of 

 dollars have been lost needlessly in exploit- 

 ation by not understanding or paying atten- 

 tion to this matter. In many cases it can 

 be ascertained to which of these three classes 

 an ore deposit belongs. 



The character of a deposit in most cases 

 will determine this. 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 exploration may be war- 

 ranted, although, as already pointed out, 

 such deposits may decrease in richness 

 with depth. Where a deposit is pro- 

 duced 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 be- 

 longs 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 du- 

 plicated 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 pros- 

 pecting of the lean pyrrhotite in the Appa- 

 lachian range will doubtless agree to this 

 statement. Deposits produced by two con- 

 centrations may grade into the class pro- 

 duced 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 redupli- 

 cated at depth. It therefore appears to 

 me that the determination to which of the 

 classes of ore deposits produced by under- 

 ground waters a given ore deposit belongs 

 has a direct and very important practical 

 bearing upon its exploration and exploit- 

 ation. 



In conclusion, I hold if mining engineers 

 and superintendents understand the work 

 of underground water, understand why and 

 how ore deposits are made, less money will 

 be expended in fruitless exploration ; money 

 will not be wasted in searching for deposits 

 at places where nature never placed a de- 

 posit. Therefore, it seems to me to be the 

 part of wisdom for a mine owner or man- 

 ager to make a complete scientific investi- 

 gation of a deposit of which he has charge 

 in order to ascertain to which of these three 

 classes the deposit belongs ; and then to 

 carry out the exploration and exploitation 

 according to the principles which apply to 

 the particular case. 



0. E. Van Hise. 



Univebsity of Wisconsin. 



