34 TlMEHRI. 
a pressure equal to eleven and a half atmospheres, still 
remains in good preservation. The report contains a 
long extract from Pliny on Gold Mining as practised in 
various parts of the world in his day. 
It would take too much space to transfer to these 
pages the interesting accounts of the vast works under- 
taken in the prosecution of hydraulic mining in California; 
and moreover this is not necessary on the present 
occasion, since the conditions under which gold is sought 
and collected in that region, differ widely from those 
existing in Guiana. It would be difficult for instance to 
transport to our gold fields iron pipes 30 inches in 
diameter, and to lay them down in lengths of several 
thousand feet. The photographs which have been kindly 
forwarded with these reports from the Bureau, shew 
very vividly this mode of applying water, and its ex- 
ceeding force. 
" Drift Mining" which is a form of placer mining, is 
the gathering gold from the bed rocks on which the 
auriferous gravel banks- lie, and which are generally 
considered to be ancient river channels. The deposits 
are worked by tunnels or drifts driven into the banks. 
"Ground Sluicing" practised only when water is 
plentiful or where the yield is not estimated to pay for 
the more expensive process, is carried on by bringing 
water in a ditch to a high point, so as to produce a 
strong current across the claim. A ditch is then dug 
which is extended by the water cutting its own way, 
aided by the miners breaking down its sides with pick 
and shovel, and if there is no rock bed at the bottom, 
one is made by throwing in stones. The ditch is 
furnished with a sluice box and riffles at its further end. 
