650 RECORD OF MEETINGS OF THE 



tions tend to restrict the activities of the meteoric waters to 

 the vadose region as Posepny calls it, i.e., that belt of the rocks 

 which stands between the permanent water-level and the sur- 

 face. Within it is an active area of solution, as we have all 

 recognized for many years, but, as previously stated, experience 

 shows that the metals which go into solution in it strongly tend 

 to precipitate at or not far below the water-level itself. 



It is of interest, however, to seek some quantitative expression 

 of the problem, and the assays given above furnish the necessary 

 data. 



I have taken the values of the several metals which have been 

 found by the assays of what were in most cases believed to be 

 normal wall-rocks, selecting those of igneous nature because 

 experience shows them to be the richest. The percentages 

 have been turned into pounds of the metal per ton of rock; 

 this latter value has then been recast into pounds of the most 

 probable natural compound or mineral in each case. I have 

 next calculated the volume of a cube corresponding to the last 

 weight, and by extracting its cube root have found the length 

 of the edge of such cube. If now we assume a rock of a specific 

 gravity of 2.70, which is a fair average value, and allow it 11 

 to 12 cubic feet to the ton, or say 20,000 cubic inches, the 

 edge of the cube-ton will be 27.14 inches. The ratio of the 

 edge of the cube of metallic mineral to the edge of the cube-ton 

 of enclosing rock will give us an idea of the chance that a crack 

 large enough to form a solution-water-way will have of inter- 

 secting that amount of contained metallic mineral. Of course 

 in endeavoring to establish this quantitative conception I realize 

 that the metallic mineral is not in one cube, and that through 

 a cube-ton of rock more than one crack passes; but I assume 

 that the fineness of division of the metallic mineral practically 

 keeps pace with the lessening width and close spacing of the 

 crevices. It is also realized that the shape of the minerals is 

 not cubical. I am convinced from microscopic study of rocks 

 and the small size of the metallic particles that their subdivision 

 certainly keeps pace with any conceivable solution-cracks, and 

 that no great error is involved in the first assumption made. 

 The sides of a cube represent three planes which intersect at 



