J. \V. SPENCER — THE IROQUOIS SHORE. 195 



Mr. Gilbert's suggestion, in connection with the second paper, — that the valley 

 south of the divide was filled with ice, and that the terrace, 200 feet below the highest) 

 indicates the coursing of a river between the ice and the side of the valley, eroding 

 the drift-floor and forming a parapet only one or two feet high, — should be placed 

 alongside of the explanation of the cleaning out of all the drift from the summit of 

 the col, where the current must have been more sluggish, by a glacial river. The 

 object of this paper is only to point out a conspicuous example where terraces do 

 occur upon the southern sides of the valley divides, in regions of reputed glacia' 

 lakes, and therefore the absence of the terraces upon the southern sides of divides 

 must be proved and not simply asserted. 



President Gilbert resumed the chair, and the following paper, the illus- 

 trations of which had been exhibited the preceding evening, was then 

 read : 



THE GEOLOGY « » 1 THE CRAZY MOUNTAINS, MONTANA. 



BY .1. E. WOLFF. 



« 



Remarks were offered by J. S. Oilier, G. K. Gilbert, B. K. Emerson 

 and Arthur Winslow. 



The paper is printed us pages 445-452 of this volume. 



This was followed by — 



NOTES ON THE GEOLOGY OF THE YUKON BASIN. 



I!V C. WILLARD HAYES. 



[Abstract.] 



During the summer of 1891 the writer was detailed by the Director of the United 

 States Geological Survey to accompany Lieutenant Frederick Sebwatka on an 

 expedition designed to explore the southern portion of the Yukon basin, Alaska. 

 The route followed was by way of Taku liver, lake Abklen, and Teslin anil Lewes 



rivers to the confluence of the Lewes and Pelly, which form the Yukon; thence 

 s< hi 1 1 1 west ward through the basin of White river, across the interior range of the 

 Saint LI ias mountains by a pass at the bead of White river, and down Chittenah and 

 Copper rivers to the coast. The distance traveled was about 1,000 miles, over 700 

 being through unexplored country. The principal geographic results of t he expe- 

 dition are t lie approximate mapping of Taku river, lake Ahklen and Teslin river ; 

 also of a large part of the basin of White river, and portions of the Saint Elias 

 mountains. Systematic observations on the hard geology were rendered imprac- 

 ticable by the difficulties attending t ra\ el in the region traversed. The nick.- along 

 White river basin are chiefly eruptives, with a few highly altered sediments of un- 

 determined age. The interior range of the >aint Elias mountains extending north- 

 west ward toward mounl Wrangell has a simple synclinal structure and is composed 

 chiefly of Carboniferous and Triassic strata. The white volcanic tuff which has 

 been noted bj various travelers on the Lewes ami Pelly was found t" increase 

 gradually toward the west, reaching a maximum of from 50 t'> 7"> feel in thickness 

 in the upper While river valley, from that point decreasing very rapidl} west- 

 ward. The probable source of the tuff is a high conical peak in the northern 



