REPORT OF TEE CHIEF ASTRONOMER 621 



SESSIONAL PAPER No. 25a 



adjacent horst respectively. Unless Lightning creek and the Skagit river are 

 subsequent streams — which appears doubtful—, there is little stream-mileage 

 in this part of the range which can be referred to the subsequent class. The 

 recent unroofing of the Castle Peak stock has brought Castle creek locally into 

 superposed relations. As erosion progresses it is practically certain that the 

 surrounding shales will be lowered much faster than the granodiorite, whereby, 

 in the end, Castle creek will probably lose its present head and the drainage 

 of the stock will become ' subconsequent.' 



Skagit Range.— -The peaks of the Skagit range rival in height those of the 

 Hozomeen range and the strength of the relief is yet greater, for the local 

 baselevel, the Fraser river, is almost at sealevel. Sleese mountain at 7,800 feet, 

 Glacier Peak at 9,000 feet, and many other ragged horns east and west of Chilli- 

 wack lake are ascended only after climbs of from 5,000 to 6,000 feet from Chilli- 

 wack lake or river. 



The relief is again due chiefly to erosion, acting on the differ- 

 ential uplifts of an extremely complex mountain-built mass. This mass 

 is heterogeneous, though its constituent rocks are generally strong in absolute 

 measure; the relatively weak rocks are concentrated in the lower part of the 

 western slope. Not a single constructional bed-rock slope is represented in the 

 range at the Boundary belt, unless possibly the north-facing slope of the Skagit 

 volcanic mass east of the divide is a fault-scarp of comparatively recent date. 



Near the beginning of this chapter a suggestion is offered as to the diffi- 

 culty of explaining the course of the Chilliwack river. Cultus lake valley, 

 Tamihy creek, and the head-waters of the creek next on the west are located 

 on master-faults, and, with further field-work, it may be proved that other 

 drainage-lines have been similarly marked out by crustal breaks. How far the 

 actual valleys were initially determined by these faults and how far they have 

 been opened by headward growth of pre-Glacial streams which grew in length 

 with relative rapidity along the rock-zones weakened by the faulting, it is still 

 impossible to say. The genetic problem of the streams in this range is, in fact, 

 here as in so many other of the ranges we have crossed, almost completely 

 unsolved. 



Some details concerning the important topographic features induced by the 

 local glaciation have been given in the previous chapter, to which reference 

 should be made for partial information regarding this phase of the physio- 

 graphy. Other features will be discussed in the succeeding section, which will 

 deal in more general fashion with the Cascade mountain system as a whole. 



Question of a General Tertiary Peneplain in the Cascade Mountains. 



In the year 1900 Russell published an account of a reconnaissance in 

 northern Washington, in which he announced the conclusion that the Cascade 

 mountain system represents a late Tertiary peneplain upwarped and maturely 

 dissected in late Pliocene and in Pleistocene time. He writes :— 



' As described in an early portion of this paper, many peaks and ridges 



in the central portion of the Cascade mountains rise to a general uniform 



