[TYRREL1] THE GOLD OF THE KLONDIKE 37 
“Residual gravels, the rarer of the two groups and certainly the 
less extensive, are found in the immediate vicinity of the original ore 
deposits, and quite independent of water courses, viz., on mountain 
slopes, plateaus and sometimes even on mountain summits. 
“On the contrary, the gravels formed by the transporting and 
washing action of water are found only in the channels of brooks and 
rivers, in fresh water lakes or along the sea-coast. They lie for the most 
part within the present valleys or along the present shore, but are also 
often found in stretches of fluviatile sediments, sometimes intersecting 
the present direction of the valley on old river terraces, or in sheets 
covering plateaus (California, Ohlapian in Transylvania) and finally 
in old shore terraces above the present level of the sea. Their material 
is always much rolled, and for the most part is assorted, according to 
the size of the ingredients, into shingle, gravel, sand, clay, mud, etc.”’ 
The Yukon Placer Mining Law gives the following definition:— 
“Placer Ground means any natural stratum or bed of earth, soil or 
gravel, containing gold or other valuable mineral or stones, derived from 
the disintegration of older deposits, and transported to, and concentrated 
in, their present position by the mechanical agency of water, but does 
not include mineral in place, or as defined in Part III, or the disin- 
tegrated portion of a vein, lode or rock, lying above or about such vein, 
lode or rock and clearly derived therefrom.” This is entirely too narrow 
for a general definition of Placers, because, while those in the Yukon 
have been chiefly formed and concentrated through the agency of 
water, some few are composed of residual or slidden material, while in 
other countries instances have been recorded of Moraines formed in 
front of a glacier being profitably worked as Placer Ground. If amended 
by the addition of the words “or other natural forces “after” agency 
of water” the definition would be improved. 
Generally speaking, however, the Placers of the Yukon are gravels 
which have been formed by the wearing down and redeposition of the 
rocks of the immediately adjoining country. 
Of the processes which enter into the formation of Placer deposits, 
the following are the most important:—First, Rock decomposition and 
disintegration, or weathering; Second Transportation; Third, Concen- 
tration; and Fourth, Deposition. 
Decomposition and Disintegration.—In considering the disintegra- 
tion or decomposition of rocks, and especially of the igneous rocks in 
which the component particles lie close together, it must be borne in 
mind that these particles are as a rule composed of different minerals 
which differ in structure, hardness, coefficient of expansion with heat 
and cold, solubility etc. 
