[TYRRELL] THE GOLD OF THE KLONDIKE 33 
the great valleys were marked out, and “The Second Cycle of Erosion” 
was inaugurated. 
During this Cycle of Erosion the sides of the valleys were worn 
down by rain and atmospheric agencies to gentle slopes,and the country 
received something like its present configuration. In the bottoms of 
the valleys extensive gravel deposits were accumulated, these deposits 
being what are now known as the “ White Channel Gravels.”’ 
The exact age of these gravels has not been definitely determined, 
as no recognizable fossils have been found in them, but from their 
general character and position they are considered to be of Pliocene age. 
The Second Cycle of Erosion appears to correspond in a general 
way with Diller’s Sherwood Peneplain in California, on which most of 
the high level gravels of that State were deposited, though the 
resultant gravels would here appear to be of Pliocene rather than of 
Miocene age. 
The Yukon country can hardly be said to have been reduced to a 
peneplain at this time; but in order that the period may be definitely 
referred to it may be here called the “ White Channel Period.” 
The valley of Flat creek would seem to have existed previous to 
this upheaval, for deposits which appear to be of about this age are 
extensively developed in it, and the great valleys of the Yukon and of 
the Klondike may also have been marked out previous to this time; 
but as yet no deposits of that age have been definitely located in them, 
and such deposits must necessarily have been formed if these valleys 
existed. 
When the “Second Cycle of Erosion” began, and the land was 
raised to a higher level above the sea than it had occupied during the 
formation of the Dome Peneplain, old streams were rejuvenated or 
new ones were formed. Of these the Yukon river seems to have been 
the largest and it at once began the downward erosion of its valley, 
while the water which fell as rain on the adjoining highlands carved 
out smaller valleys to carry the drainage to the larger river. These 
small streams, such as Bonanza, Bear, Hunker, Dominion creeks, etc., 
which radiated from The Dome, kept excavating their channels to keep 
pace with the lowering of the bottom of the valley of the Yukon river, 
which was the master stream into which they flowed. 
During all this time the valleys of these smaller streams maintained 
the general character of gulches or young valleys, with V-shaped cross- 
sections. But little gravel or loose material remained on the rock which 
formed the bottoms of their channels, for it was being constantly moved 
downward by the current towards the Yukon river, and, on the way, 
was helping to cut deeper and deeper into the rock over which it travel- 
led. 
