GEOLOGY OF THE KLONDIKE GOLD FIELDS. 309 



of it on its shoulder, and I have also seen it in an excavation on the 

 loftily located Claim 71 of that stream. Nearly abreast of the in- 

 ternational boundary, the one hundred and forty-first meridian of 

 west longitude (Greenwich), McConnell and Russell noted the ter- 

 race line of the Yukon River as high up as seven hundred and thirty 

 feet, which is still about four hundred feet below the point where 

 I obtained wash gravel on the peak back of Dawson ; but Dr. George 

 Dawson found the terraces on Dease Lake to rise to thirty-six hun- 

 dred and sixty feet, and elsewhere he calls attention to having come 

 across water-rolled gravel at an elevation of forty-three hundred 

 feet, which would probably exceed by about six hundred feet the 

 culminating point of Dome Mountain. Such high water could, with 

 the existing configuration of the land surface, hardly define any 

 other feature than that of a large interior sea or of a series of lake 

 basins; and while it may be argued that there has been sufficient 

 degradation of the land surface since the period of the height of 

 water to permit us to reconstruct a contour that would be in har- 

 mony with altered and reduced river courses, and relieve us from 

 the necessity of invoking the assistance of lacustrine bodies in a 

 solution of the problem, it does not seem to me likely that this has 

 been the case. The physiognomy of the upper Yukon Valley sup- 

 ports this contention, and even to-day the river has not yet fully 

 escaped from a lacustrine condition which is merely fragmental of a 

 previous state. 



On one point bearing upon the succession of events in the upper 

 Yukon Valley, and which has its connection with the history of the 

 Klondike region, my conclusions differ somewhat from those that 

 have been expressed by Dawson. This pertains to the deposit of 

 volcanic ash which is so marked a feature of the accumulations of 

 the river's banks. For nearly three hundred miles by the course of 

 the river a stratum of pumiceous ash, ordinarily not more than 

 four or six inches in thickness, constitutes almost without break 

 the top layer but one of the banks on either side, and that which is 

 above it is generally only the insignificant soil or subsoil which im- 

 mediately supports the vegetation. So persistent is this ash layer, 

 and so uniformly does it hold to an even thickness and to its exact 

 position beneath the surface, that without further examination one 

 would be tempted to believe from a little distance that it was merely 

 the ordinary subsoil layer from which the color had been leached 

 out by vegetable growths. Here and there, where there have been 

 local disturbances or water washings have produced concentration, 

 it may have acquired a development of a few feet, and occasionally 

 it has accommodated itself to flexures or saggings of the deposits 

 which it normally caps as a horizontal zone. Dr. Dawson, in com- 



