La Follette, Robert M. (Robert Marion), 1855-1925, ed, La Follette, Robert M. (Robert Marion), 1855-1925, Handy, William M, Higgins, Charles · Chicago : Making of America · leaf 246
WORLDS PRODUCTION OF SILVER … GOLD AND SILVER MINING 205 tion was turned to (loop l^ing auriferous pjravels which areoverlaid by a capping of volcanic rock or by a deep stratumof barren gravel. These mines are worked by drifting. The drifting process consists in running long tunnelsunder the lava capped divides and tapping the…
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