The Tufa traced to its Source. 149 



but this is clearly impossible, as it lies wholl}^ beyond the area 

 covered by the deposit. 



The strong winds prevailing in the upper White River valley 

 during August, 1891, were from the west and Avere evidently in 

 the same direction during the great eruption. It would be 

 interesting to fix the date of the eruption, but it is impossible to 

 do so with any degree of certainty. From a study of the rela- 

 tions of the tufa bed on the Pelly and Lewes Dr Dawson says : 

 " While the eruption must have happened several hundred 

 years ago, it can scarcely be supposed to have taken place more 

 than a thousand years before the present time." A similar con- 

 clusion is reached from a study of the deposit in the White 

 River basin. As already stated, for ten miles on either side of the 

 maximum thickness the surface tufa is unconsolidated and sup- 

 ports only a very scanty vegetation ; but the tundra moss covers 

 with great readiness even the most barren surfaces, wholly inde- 

 pendent of soil, so that it seems impossible this should have 

 remained bare for any great length of time. 



From its position near the greatest thickness of the deposit a 

 vast quantity of the tufa must have fallen on the surface of the 

 Klutlan glacier as well as on the neve fields at its source. The 

 fact that this has nearly all been deposited in the terminal moraine 

 and remains only on the surface of the stagnant ice a short dis- 

 tance back from its front indicates, an interval since the eruption 

 sufficiently long for ice which then formed the neve to flow the 

 whole length of the glacier and deposit its burden in the termi- 

 nal moraine. Neither the length of the glacier nor the rate of 

 motion of its different parts is known, but the time required for . 

 the transfer of material on the neve fields to the terminal moraine 

 must be at least several hundred years. The time since the 

 eruption has also been sufficient to permit the recession of the 

 glacier front about three miles. 



The color of the waters of White river has been noted by all 

 travelers on the Yukon who have passed its mouth. Schwatka* 

 describes it as resembling " a river of liquid mud of almost 

 white hue," and McConnellf says : " The turbid character of the 

 White river is famous, and sufficient sediment is brought down 

 to change the color of the whole Pelly-Yukon flood from a pale 



* Along Alaska's Great River : New York, 1885, p. 240. 

 t Report of an exploration in the Yukon and Mackenzie basins, N. W. 

 T. : Ann. Report Geol. Surv. Canada, Montreal, 1891, p. 144D. 



•21— Nat. Geog. Mag., voi,. IV, 1892. 



