248 GEOLOGY OF THE BLACK HILLS. 



five men for ten hours, the result was $3.24 per day per man, and with 

 economical and skilfull working on a larger scale the clean-up should equal 

 at least one-half ounce, or $10, to the hand. The soldiers had been panning 

 previously from this spot for two weeks and worked out the richest of the 

 gravel, and on weighing the gold in their possession I found that they had 

 obtained about $32 from the area I had sluiced in both da}^s' work, which 

 measured 216 square feet and had been excavated 18 to 20 inches in depth; 

 or 12 cubic yards of gravel put through the sluice had yielded $16.20 in 

 addition to that obtained by the soldiers, giving $48.20 as the total yield, or 

 about $4 per cubic yard. The water leaking into the pit gave a great deal 

 of trouble, preventing the bed-rock from being properly cleaned up, and 

 the blue plastic clay, on being shoveled into the sluice, even after puddling, 

 rolled into balls and washed through the boxes unchanged, carrying with 

 it any gold which it contained. On testing the tailings which concentrated 

 under the tail of the sluice, I found that considerable gold had in this way 

 been swept through and lost, the sluice being too short to properly work 

 so clayey a gravel. The soldiers rockered the heaviest of these tailings 

 and the lumps of clay, obtaining about \ pennyweight of scale gold from 

 them. Large quantities of red garnet crystals were caught in the riffles, 

 together with cubical crystals of iron pyrites and round water-worn pieces 

 of hematite iron ore. No quicksilver was employed, as I wished to pro- 

 cure a sample of the gold in its natural state for assay. 



The richest layer in the deposit was the lower part of the red garnet 

 gravel where it rested on the upper surface of the blue plastic clay. Pieces 

 taken from this contact showed, on breaking, scales and particles of gold 

 contained in it. The bed-rock, as far as we dug into it, about a foot below 

 its surface, contained coarse gold in small quantities, probably caught in 

 crevices in the rock before it decomposed. The soldiers, under the direc- 

 tion of John Roberson, for two days sluiced the gravel from the bed of the 

 creek below the riffle, but found the bed-rock either a hard massive quartz- 

 ite, worn by water smooth and level, or a ferruginous quartz with masses 

 of crystalline iron pyrites — the outcrop in the creek of the Mammoth ledge. 

 The gravel was loose and poor in gold, and the character of the bed-rock 

 prevented it from ever retaining any gold swept over its surface by the 



