20G ANNALS NEW YORK ACADEMY OF SCIENCES 



peaks of about the same elevation rise in the distance, Ijut none high 

 enough to cut off the vista of still more distant peaks. More than 100 

 miles to the north the volcanic cone of Mt. Baker and an equal distance 

 to the south Mt. Eainier loom uj) into the field of one's vision as the eyes 

 rest on the mountainous landscape. The enchanted mountaineer is im- 

 pressed with the nearness of these majestic, pure white cones, and the 

 idea occurs to him that if only one could fill the depressions between 

 peaks, the surface would be practically level. If such a thing were 

 actually done, the result would be what physiographers call an upraised 

 l^eneplain (Fig. 1). 



^ The existence of this peneplain is generally admitted. EusselP called 

 it the "Cascade Plateau" and various subsequent writers have used the 

 first half of the term, replacing the second with such equivalent terms as 

 "uplift" (Willis).^ This uplifted peneplain will be called the^ Cascade 

 peneplain for the purjooses of this paper. 



The character of the deformation resulting in the plateau must be 

 worked out from a study of the range as a whole, 300 square miles being 

 too small an area in which to do more than apply such principles. These 

 j^rinciples are two in number : 



1.^ The cause of uplift of the Cascade peneplain is to be found in com- 

 pressive stress acting on materials below the outer crust, the surface 

 deformations being incidental results of such deep-seated strains. 



2.^ The slow and gradual uplift of the peneplain was accompanied by 

 local warpings whose parallel axes lie at an angle to the j)rincipal axis of 

 the uplift. 



Granting the first of these principles, the second needs no further 

 proof, since any irregularity in the surface, in the competency of the rock 

 structure or in the direction from which the pressure of deformation was 

 applied, would result in such warpings of the surface. 



The northernmost warping in the Snoqualmie quadrangle is called the 

 Wenatchee Uplift. Trending west of north, this uplift included all of 

 the mountains south of the Skykomish Eiver lying in the Skykomish 

 quadrangle. The mountains north of the Skykomish Eiver seem to l)e- 

 long to a separate uplift. Weaver has called them the Skykomish Moun- 

 tains (Fig. 2) and they will here be called the Skykomish Uplift.*^ The 

 presence of the well defined Skykomish Basin, with its gentle slopes rising 

 southward and its steeper slopes rising northward, seems sufficient e\'i- 



2 I. C. Russell : 20th Ann. Report, U. S. G. S., pt. 2, p. 144. 



3 Bailey Willis : U. S. G. S. Prof. Paper 19, p. 85. 1K03. 

 ^Idem: Prof. Paper 19, 1903, p. 97. 



5 Idem: Prof. Paper 19, 1903, p. 97. 



"C. E. Weaver: Bull. 7, Wash. (ieol. Sarv., p. 31. 1911. 



