372 The American Geologist Tune, 1992 
Notes 1—In case of No. 1, rivers frequently cut gold bearing 
veins in their courses. This seems to be the only plausible ex- 
planation of the occurrence of gold beds on Snake river, Idaho; 
these beds in which the gold is found on the surface are far re- 
moved (in some cases, forty or fifty miles) from their sources. 
No. 3.—These gravels have been no doubt rearranged by action 
of water, presumably by a lake. 
No. 4.—The vein, owing to decomposition and disintegration 
may be converted into soil or quartz pebbles to considerable depth, 
the quartz pebbles frequently containing native gold, showing a 
slight attrition. 
The method of arrangement of gold in placers, depends on 
various conditions which can hardly be considered sufficient basis 
for classification. Thus its comparative depth in the gravels, its 
tolerably uniform dissemination, or local occurrence, its physical 
characters, ete., depend on such forces as gravitation, distance 
from source, denuding forces, time of denudation and deposition; 
and these different methods of occurrence may be found indeed 
in any of the varieties of placer beds. As regards the nature of 
the force which brings down the material from the mountains, and 
causes the rounding of the rock fragments, it may be of a varied 
character and admit of classification. 
1. The melting of snows and rainfall, producing spring freshets 
and streams. 
2. Glacial action, This must have been a very common 
agency from the evidence obtained. 
3. Gravitation. A natural settling down of rock fragments 
loosened by chemical disintegration to a lower level. This is 
largely aided by the percolation of waters. 
With regard to this latter method of forming placer beds, Hay- 
den, in his report on Geology of Colorado, refers to the force of 
gravitation as not unusual in the formation of gravel beds and 
banks along the bases and flanks of mountains. The character 
and great extent of many gravel beds, show very plainly that the 
denuding agencies must have been very active at one time in the 
recent history of the hills. This seems to be best explained by 
the action of glaciers which during the glacial period must have 
covered the mountains and caused during their recession in a 
more genial climate the immense beds of detritus which the 
rivers and streams flowing fromthem piled up in the valleys below. 
