624 DEPARTMENT OF TEE INTERIOR 



2 GEORGE V., A. 1912 



Reasoning on this basis. Russell concludes that most of the larger streams of 

 the Cascades, like the Skagit, Methow, Chelan, Yakima, etc., are of consequent 

 origin. ' Their courses were determined, in the main at least, by the surface 

 slopes of the Cascade peneplain.'* 



Two years before Russell began his reconnaissance, Willis had come to very 

 similar conceptions of the later geological history of the Cascades. These 

 views were strengthened during several visits to the field between 1895 and 

 1900, inclusive. In collaboration with G. 0. Smith, Willis published ' Contri- 

 butions to the Geology of Washington/ in which the hypothesis of late Tertiary 

 peneplanation was considerably amplified, f Again somewhat liberal quotations 

 will be made, as this paper, like Russell's bears directly on the geology and 

 physiography of the Forty-ninth Parallel in the Cascade system: — 



' Among the services rendered the writer [Willis] by George Otis 

 Smith was that of well maintained scepticism in regard to recognition of 

 an ancient plain over the Cascades. He asked for demonstration, which 

 was difficult, since the suggestions of panoramic views failed to convince, 

 but during his field work of 1900 he himself supplied the evidence of an 

 old base-level plain on the hills of Yakima valley, as stated in the first part 

 of this paper.' 



After giving an analysis of the topography in a large, typical area of the 

 Cascades, Willis writes : — 



1 Enough has been said in the descriptions to indicate that several 

 stages of topographic development have been recognized. They are clearly 

 evident in such a profile as No. 1, PI. XIX., from the Entiat mountains 

 across Columbia canyon to Badger mountain. Beginning with the highest, 

 the peaks (5,700 to 5,800 feet) and the flat adjacent to them are considered 

 to be representatives of the oldest stage of which definite evidence remains. 

 They are correlated with Badger mountain, the Waterville plateau, surfaces 

 in the Chelan and possibly the Methow mountains, and the level from 

 which the high Cascades are sculptured. This oldest stage is therefore 

 that of the Cascade plateau, as named by Russell, but now called the 

 Methow stage. It is also identified by G. O. Smith. The characteristic 

 topographic type of the Methow stage was a plain, upon which residual 

 hills survived. Following Davis, it may be designated a peneplain, with 

 monadnocks. 



' Within this plain were carved valleys which appear to have attained 

 nearly mature development. That of the Columbia in profile No. 1" PI. 

 XIX., appears to have been 2,000 or 2,500 feet deep and seven or eight 

 miles wide. The smaller streams certainly developed shallower and narrower 

 valleys, but remnants of the Methow plain west of the Columbia were few 

 and limited. On account of its preservation in the basin of the Entiat, 

 this stage is named from that river. The characteristic topographic form 



* T. C. Russell, Twentieth Annual Report, U. S. Geological Survey, Part 2, 1900„. 

 pp. 140-144. 



f B. Willis, Prof. Paper No. 19, U.S. Geol. Survey, pp.' 48 and 68-70. 



