3°4 



LEWIS G. WESTGATE 



Afa>»i 4tre<wn. 



Fig. 8. — Diagram of hanging valley. 



near Everett, an extensive area of glaciated ledges on the south side 

 of the valley shows the ledges sloping to the east — again an expression 

 of rock-jointing, which in this case holds a different direction from 

 that farther down-stream. Facts of this kind, occurring through the 

 valley, point to glacial plucking as being as important as, perhaps 



much more important 

 than, glacial abrasion 

 in the erosion of Lake 

 Creek valley. 



Other minor features 

 of glacial smoothing are 

 illustrated at different 

 points in the main val- 

 ley. Evenly rounded ledges of considerable size, shallow saucer- 

 shaped (in cross-section) furrows, glacial undercutting, and in some 

 cases a smoothing of parts of the protected lee sides of eminences, 

 also occur. A feature noticed in one or two cases was the production 

 of nearly flat, smoothed surfaces intersecting at a small angle, and 

 separated by a sharp ridge, the whole being worked out of sound 

 rock. Evidently some change in the current of the ice had taken 

 place at that point. Of similar nature is the gouging of a flat sur- 

 face by a shallow groove, much as a shallow groove might be cut in 

 a planed board by a gouge of large curve. 



3. Hanging valleys and truncated spurs. — When the main valley 

 of a preglacial drainage system has been deepened by glacial erosion, 

 the relations which should exist after the disappearance of the ice 

 may be represented by Fig. 8. The spurs of the old divides and 

 the lower ends of the tributary valleys have been cut away, giving 

 hanging valleys and truncated spurs. It is not essential that the 

 upper limit of glaciation should coincide with the level of the lateral 

 valley, as it does in this figure. The tributary valleys may or may 

 not have been occupied by glaciers. If they have been so occupied, 

 the form of the hanging valley will be like B in the figure, broad and 

 U-shaped; if not, like A, more or less broadly V-shaped, according 

 to the steepness of the preglacial valley. Terminal facets marking 

 truncated spurs, and both glaciated and non-glaciated hanging val- 

 leys, are found along the sides of the Lake Creek valley. 



