44 THE ROYAL SOCIETY OF CANADA 
area since the downward erosion of the Dome peneplain was 
inaugurated. 
The work of removing this enormous quantity of rock must have 
taken a very long time, for it is not likely that rock weathers as quickly 
in that far Northern country as it does farther South, and streams which 
are frozen to the bottom for half the year cannot cut down their valleys 
as quickly as those which have the whole year to work in. Besides 
that, the ground in the north has a tendency to be covered by a thick 
growth of sphagnum moss and other low vegetable organisms which 
prevent the water from wearing the surface away. In the valley of the 
Mississippi it has been found that the country is being worn down at an 
average rate of about one foot in 4,000 years. If this rate is applied 
to the Klondike district it would mean that it has taken 3,600,000 years 
to reduce the Dome Peneplain down to the present configuration of the 
country. However, I am satisfied that the Yukon river does not carry 
away as much sediment as the Mississippi, and especially is this so if the 
glacial mud, which is brought down by the White river and other similar 
streams from the mountains, is eliminated from the computation. If 
the Yukon and its tributaries have eroded and reduced their valleys 
in past times at the same rate that they are eroding to-day, it is probable 
that a rate of one foot in 6,000 years, or even more, should be applied, 
in which case the time needed for the erosion of the Klondike district 
to its present shape would be 5,400,000 years or more. 
Concentration and Deposition. I have shown that the Klondike 
area was gradually worn down as an individual unit from the Dome 
Peneplain to its present shape in two successive periods, which have 
been here called respectively the ‘‘ White Channel Period” or “Second 
Cycle of Erosion” and the “Recent Period” or “Third Cycle of Ero- 
sion.” Both these periods may have been made up of two or more sub- 
periods, though that question has not been discussed here. Of the two 
main periods, the former, or White Channel Period, was very much the 
longer, and the greater portion of the erosion was performed during it. 
While the erosion was in progress the eroded material was being 
carried down into the valleys and thence outwards to or towards the sea. 
At first the streams were actively deepening or wearing down 
the bottoms of the valleys. Therefore these valleys were in the form 
of V-shaped gulches, from which all the finer and lighter material was 
being carried away, while the heavier particles, such as gold, magnetite, 
etc. were being scattered along the bottoms of these narrow valleys. 
The particles of gold contained in the gravel or sand would be 
carried along by the water of the streams, over any smooth rock, until 
they would settle into crevices in the rock itself or into spaces between 
