212 ANNALS NEW YORK ACADEMY OF SCIENCES 



The type of drainage in the Skj'komish Basin is medium textured and 

 its pattern is dendritic. Of the 300 square miles included, ybtj few have 

 no stream of mapable size, Avhile inanj have as many as six. The master 

 streams have a course oblique to the trend of the mountains. The sec- 

 ondary streams are parallel to the axial trend and those of lesser order 

 are dendritic. The South Fork of the Skykomish and the Middle Fork 

 of the Snoqualmie are the master streams. 



Erosion of the Cascade Mountains had reached a mature stage before 

 their occupancy by glaciers. These glaciers continued their work long 

 enough to destroy nearly all the pre-giacial upland (Fig. 6) and so reach 

 a stage of maturity. Present day drainage is largely throiigh glacial 

 troughs which are characterized by precij)itous canyon walls, hanging 

 valleys and some undrained SAvamps and numerous lakes. 



Eelatiox of Topography to Geology 



We have seen that the major Cascade peneplain had warpings whose 

 axes were oblique to the principal Cascade axial trend. Two of these 

 warp'ings, which seem to be identifiable in the area imder discussion, we 

 have called the Wenatchee and the Cascade Mountains. We have seen 

 that these warpings have a gentler slope toward the north. The possi- 

 bility that the steeper sloj^es might be fault escarpments lias been pointed 

 out by Weaver,^^ but neither he nor any other writer have found any 

 direct evidence of faulting and at present the unsymmetrical fold hy- 

 pothesis seems more defensible. 



It seems possible that some relation exists between the present drainage 

 system and the original structure of these folds. Some future work may 

 explain this relation, but at present insufficient information is at hand to 

 justify any genetic classification of the rather comi^lex drainage system. 



Streams and glacial corrosion have produced many sharp peaks. The 

 highest of these is 7986 feet in elevation and lies on the divide betAveen 

 the Columbia and the Puget Sound Avatersheds. A tew other elevations 

 reach 7000 feet or over and many lesser peaks approach this height. All 

 those above 7000 feet are on the Cascade Divide, a condition which is 

 not in accord Avitli Smith's observations in the Snoqualmie Quadrangle.^ '^ 



The relation betAveen kind of rock and type of to230graphy must be 

 stated cautiously. It is notable that the higher mountains, such as Big 

 SnoAV, Index and others, are in plutonic igneous rocks. But on the other 

 hand. White Horse Mountain is in Eocene sandstone. The high peaks on 



T''C. K. AVeaver : Index Mining District, P.ull. 7. AA'asli. Gool. Surv.. p. 32. 1012. 

 "Geo. (). S-NriTiT : Contrilnitinns to the lifolopy <i1' AA'asliiiigton, Piof. Paprr 10, pp. 

 et sei/. mo-'i. 



