Gold Mining Notes. 33 
Placer Mining is " the gathering by mechanical means 
" of native or free gold found disseminated in alluvial 
" deposits in certain parts of the earth's crust." Every 
variety of placer mining is based on the fa6l that gold 
is heavier than most other metals or substances. 
In placer mining the auriferous material is obtained 
by digging up the surface, or in larger operations by 
hydraulicing, as it is termed — drifting, blasting, sluicing 
and other modes. 
Hydraulic mining occupies much of the Reports under 
contribution, for although it has been recently prohibited 
in the State of California because the debris resulting 
therefrom was found to be detrimental in many ways to 
many interests, it was the easiest and cheapest way of 
disintegrating the gravel banks in which the gold was 
richly deposited. 
" Hydraulic Mining" is defined as the application of 
natural forces to move large quantities of earthy matter 
and the collection of a certain quantity of gold too 
small to be profitably severed by other and easier methods. 
To be successful, certain conditions only to be found in 
a newly settled mountainous country are required, namely, 
an abundant supply of water, a deposit of loose, easily 
disintegrated earth, containing a paying quantity of 
gold, a bed rock not too deep below the surface, a 
channel into which the debris can be discharged, and 
high ground above the drains to which water can be 
conveyed to give the required pressure. This system of 
mining was known to and practised by the ancients, and 
an aqueduct built at Alatri in Italy 200 years B.C., of 
earthenware pipes imbedded in concrete for eleven 
and a half miles, capable of sustaining at its lowest point 
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