[TYRRELL] THE GOLD OF THE KLONDIKE 45 
or among large loose rock masses, from which places they could not be 
dislodged except by upward currents. Such currents would first lift 
pebbles of quartz or similar rock less than five times the diameter of 
nuggets or particles of gold, before they would lift the particles of gold, 
even if the quartz and gold were equally accessible. But as a rule 
they are not equally accessible, for the lighter rocks being larger would 
stand higher than the particles of gold, and the spaces between them 
would hold and protect the smaller masses of the heavier metal from the 
current. 
Thus the removal of gold by currents, after it has once been lodged, 
becomes exceedingly difficult as long as the crevices or spaces in which 
it is lodged persist. 
While astream keeps cutting its channel downwards new crevices 
or lodgment places are being constantly developed in the rock beneath 
the old ones which are being cut away. The gold keeps working down 
or dropping into them, and thus it moves almost vertically downwards 
with the deepening of the valley. In this way a streak or band of rich 
gold-bearing gravel would be formed in the bottom of the narrow 
valley, distributed in the crevices of the rock and in protected places 
immediately on top of it. 
After the stream had cut the bottom of its valley down to grade 
or base level, and had ceased the process of vertical erosion, it would 
begin to cut laterally and to widen the bottom of the valley so formed, 
and to deposit sand and gravel in the form of flood-plains on it. 
During this process of lateral erosion, the gold, which had already 
been collected from all the surrounding country into the bottom of the 
V-shaped valley, would be, to a large extent, below and out of reach 
of the influence of the meandering stream with its slower current. The 
stream would, however, continue to widen its valley and to extend its 
flood-plain and in many cases to build this flood-plain up to greater 
and greater thickness. 
In this way we can see how such pay-streaks as that of the White 
Channel gravels of Bonanza Creek have been formed. They represent 
the gold collected in the old V-shaped valleys of that period, while the 
great thickness of gravel above and on both sides of them was deposited 
after these pay-streaks were formed. 
Gold is usually not entirely absent from the upper and lateral 
gravels, for some of the precious metal was being constantly washed 
down from the adjacent hills with pebbles of quartz, schist, and other 
rocks; but the coarse gold of the pay-streak on and in the bed-rock was 
collected into its present position before the gravel was deposited on 
top of it, and it was not concentrated out of the gravel above it, as has 
often been assumed. 
Sec. IV., 1912. 4. 
