372 RESUME AND THEORETICAL DISCUSSION. 
At the “ No. 8”? mine of the North Bloomfield Gravel Mining Company,* 
during the time from Jan. 1, 1875, to Oct. 18, 1877, 7,071,630 cubic yards 
of gravel were washed with an expenditure of 5,750,797,560 cubic feet of 
water. This gives an average of 534 cubic feet of water required to wash 
one cubic yard of gravel; or, in other words, the gravel at this locality 
required for moving it an expenditure of water nearly equal to twenty times 
its bulk. At the Blue Tent Company’s mine, where careful record has been 
kept of the amount of gravel washed, water used, etc., for the past few years, 
the various kinds of gravel met with were moved at the rate of from 2.38 to 
10.12 cubic yards per miner’s 24-hour inch; f or, in other words, the gravel 
required, according to its condition, from eight to thirty-four times its volume 
of water to disintegrate it and carry it into the sluices. That which demanded 
the largest quantity of water specified is described as being “ hard, indurated, 
and clayey.” 
Mr. Hague adopted seven cubic yards as the amount of gravel which, on 
the average, in the divide between the South and the Middle Yuba, could be 
moved by a 24-hour inch of water, and this is said by Professor Pettee to 
be corroborated by the results obtained at Smartsville. Seven cubic yards 
to the 24-hour inclt gives an amount of gravel not quite one twelfth of the 
volume of the water used.§ 
Mr. Ashburner considered that a 24-hour inch of water would move only © 
about three and a half cubic yards of the lower portion of the gravel deposit 
in Bear River and its tributaries. This gravel may be considered as repre- 
senting the hardest kind ordinarily worked by the hydraulic method. + | 
It appears, therefore, that a 24-hour inch of water will disintegrate and 
* The writer is indebted for these statistics to the kindness of Hamilton Smith, Jr., Esq. 
+ A miner’s inch flowing for twenty-four hours is considered on the San Juan Divide equal to 2,230 cubic feet 
of water ; in the Bear River mines it is a little less (about 2,200). The difference arises from the different forms 
of opening for the water to pass through, and the variable number of inches pressure allowed. 
¢ See ante, p. 207. 
§ The following extract from Mr. Hague’s report, to which reference has before been made, states clearly and 
concisely the main facts relating to the use of water by the hydraulic method : ‘‘ At the present day the diameters 
of the nozzles vary from five to eight inches; the pressures under which they are used, at various places, from 
150 to 400 feet; the velocity with which the water is discharged may vary from 75 to 150 feet per second, accord- 
ing to the pressure ; and the quantity of water thus discharged through one nozzle, according to all these varying 
conditions, ranges from 300 or 400 to 1,200 or even 1,500 inches. A discharge of 1,000 inches in a single stream 
is not unusual. The volume of water thus discharged is 1,570 eubic feet per minute, weighing but little less than 
100,000 pounds. The water used in the actively working mines on the ridge [the San Juan Divide, or the 
district between the South and the Middle Yuba] at present varies from 500 or 600 inches running ten hours, to 
3,000 inches running twenty-four hours.” 
