GEOLOGY OF THE KLONDIKE GOLD FIELDS. 313 



Let us examine the possibilities of the case. As an initiatory 

 premise it might be assumed, without much chance of either affirma- 

 tion or denial, that the degradation of the land surface in the imme- 

 diate valleys of the main streams is or has been in the past taking 

 place at the rate of half a line per day; so far as the eye and ordi- 

 nary instruments of measurement are concerned this is a quite in- 

 appreciable amount, and I see no reason why it may not be assumed 

 as the working power of the Yukon. "With this rate of erosion a 

 valley trough or contour of about a foot and a third might be 

 formed in the period of a single year, or of nearly seven hun- 

 dred feet in five hundred years; and if we lessen the daily ero- 

 sion to one quarter of the amount stated i. e., to an eighth of 

 a line we should still have in this same period of five hundred 

 years, speaking broadly, a trough of about one hundred and seventy- 

 five feet depth, quite sufficient to have brought about most marked 

 changes in the aspect of a drift-covered lagoon region, and perhaps 

 ample to account for those physiognomic peculiarities which have 

 been discovered. I am fully impressed with the magnitude of the 

 distance which separates the amount of erosion which I have as- 

 sumed an eighth of a line daily from the " one foot in six thou- 

 sand years," which has been preached categorically from lecturn 

 and text-book for the better part of a quarter of a century and 

 threatens to make dogma for still another period of equal length; 

 but the conditions here are entirely different from those of average 

 continental denudation in fact, have as nearly nothing in common 

 as they can have. My observations in the tropics and subtropics 

 have most impressively taught me the lesson of rapid changes, and 

 with the conditions that are and have been associated with the 

 Yukon, I am prepared for the lesson of equal change in the north. 

 But, as a matter of fact, are we not taught of a removal in the west 

 central United States of some twelve thousand feet of rock strata 

 in a period not impossibly considerably less than two hundred thou- 

 sand years? The one foot in sixteen years has here likewise noth- 

 ing in common with the " prevailing " rate of continental de- 

 struction. 



While stalled on a bar on the Yukon River, about two miles 

 above Fort Selkirk, I was much impressed with the mechanical work 

 of the stream. The gravel and pebbles were being hurried along rap- 

 idly under the lash of a five to six mile current, and their groans were 

 audible frequently when they themselves were invisible. Every 

 few minutes our steamer would swerve from her seemingly fixed po- 

 sition by the undercutting of the bar, and perhaps it would be not 

 far from the truth in saying that we should be to-day in very nearly 

 the same position that we were in then had it not been for this un- 



TOL. LV. 24 



