270 GEOLOGY OF THE BLACK HILLS. 



inches of water (August 1, 1875), which will prove useful in working the 

 gravel bars in that vicinity. 



Rapid Creek, above the springs, is a fine stream of water, from 20 to 25 

 feet wide and 10 to 15 inches deep, with a very swift current. Probably 

 the volume or the water is not less than 2,000 miner's inches in July, and 

 below the springs 2,500 inches is not too great an estimate for the available 

 water. For at least five miles along the valley below the mouth of the 

 canon the stream is bordered by the largest gravel bars and flats discovered 

 in the Hills, reaching out to the low ridges of Jurassic foothills, among the 

 level plains, and capping broad benches of limestone and Bed Beds at the 

 sides of the valley. The amount of gravel brought down by Rapid Creek 

 and piled up in these deep and extensive deposits is very large ; not only 

 low hills below the cailon are covered by high bars at several different ele- 

 vations, but the broad flats along the stream are made up of a deep deposit 

 of gravel, composed mostly of limestone and sandstone, intermixed with 

 some slate and quartz. Several attempts were made by my assistants to 

 sink prospect holes on these flats along the banks of the creek, but the pits 

 had to be abandoned at depths of from 9 to 12 feet before reaching bed- 

 rock, on account of striking springs of water. The loose gravel from these 

 holes gave one or two colors of gold to the pan, but it was probably quite 

 a distance to bed-rock where we stopped working, as the gravel was open 

 and full of small bowlders. To work these flats, if they are found to con- 

 tain gold in paying quantities, will require the outlay of considerable labor 

 or capital to drain the bed-rock, but the grade of the valley will admit of 

 long covered bed-rock drains being put in for this purpose. 



At the mouth of the cailon the stream flows along the face of the lime- 

 stone cliffs, and the largest high bars are on benches on the north side of 

 the valley, from 20 to 30 feet above the present level of the creek. Open 

 cuts were driven into these bars on bed-rock, finding nearly 20 feet of gravel 

 and about a foot of pay dirt on soft limestone bed-rock, giving an average 

 of three colors of gold, or about half a cent to the pan. Similar results 

 were obtained in prospecting several smaller gravel points at the bends of 

 the canon for a mile above these bars; and, taking into account the ease with 

 which these gravel deposits can be ground-sluiced off, with the great vol- 



