4 88 SCIENCE PROGRESS. 



of the ground rapid, and the auriferous deposits of great 

 thickness, the banks of gravel are attacked by jets of 

 water of tremendous power, and the earth washed down 

 and carried through the sluices without being touched by- 

 hand, the so-called " hydraulic method ". When the gravel 

 beds are below the general level of the country they are 

 raised by the "hydraulic elevator," a jet of water, under 

 a head of as much as 400 or 500 feet, carrying water, 

 sand, and boulders alike up a pipe inclined at some 6o° 

 to the horizon, so as to deliver them all at the head of 

 the sluice, the vertical lift being sometimes over 40 feet. 



One of the main difficulties in the hydraulic process is 

 in the disposal of the tailings, which are usually discharged 

 into a river or into the sea. The enormous amount of loose 

 sand and gravel, delivered from the hydraulic mines into 

 the Yuba and Feather rivers, California, prior to 1880, 

 filled up their beds to such an extent that in rainy weather 

 disastrous floods ensued, and much valuable agricultural 

 land was buried beneath sterile drift deposits and rendered 

 worthless. The farmers thereupon took action against 

 the mining companies and obtained a perpetual injunction 

 forbidding the discharge of tailings into these rivers. 

 The result has been to stop the use of the hydraulic 

 method in these important districts, and an apparently 

 irreparable blow was inflicted on gold winning industry in 

 California. 



In every country as soon as the richest of the placer beds 

 have been worked out, efforts are made to extract the gold 

 from quartz veins. The quartz must of course be crushed, and 

 the crushed material has in the past been generally treated 

 similarly to the auriferous sands occurring naturally. Thus, 

 according to the account given by Diodorus Siculus already 

 referred to, the quartz was reduced to coarse powder by 

 pounding it in stone mortars, then finely ground in handmills 

 resembling the flour mills of the present day, and finally 

 washed down over inclined planks with water, when the 

 lighter material was carried away and the heavy gold 

 retained on the wood. Hollowed-out stone mortars suitable 

 for the first of these operations have been found in many 



