560 WARREN S. SMITH 



In the following discussions no effort will be made to subdivide 

 the metamorphic rocks of a sedimentary origin from those of an 

 igneous origin, where these are so intimately associated as to make 

 the subdivision impracticable. However, the schists of the north- 

 eastern area are easily kept distinct from the metamorphic series 

 of the northwestern area. 



On stratigraphical grounds the rocks readily fall into two 

 groups: (1) the pre-Tertiary, and (2) the Tertiary. The division 

 line between these is the most marked unconformity in the Cascades. 

 We have present a schist, belonging to the pre-Tertiary, which is 

 cut by quartz and igneous rock dikes, making the oldest or basal 

 terrane. 



This is called the Easton schist, and it forms the metamorphic 

 terrane in the northeast. No definite idea of its age can be sug- 

 gested except that it is pre-Ordovician. Fragments of it are 

 included in the Mesozoic batholiths, and it is more complexly 

 folded than the Maloney (Gunn Peak) metamorphic series. The next 

 younger series belongs on paleontologic and correlation evidence 

 to the Ordovician. It is a series of quartzites, schists, and crystal- 

 line limestones with associated greenstones, approximately 4,000 

 feet thick, outcropping in the northwest. Weaver correlates this 

 series with the Cache Creek series as defined by Dawson. 1 It has 

 at least one stage less of dynamic history than the Easton and 

 on lithologic grounds it is believed to be equivalent to Smith's 

 Peshastin series of the Snoqualmie area; but its fossil content 

 identifies it as Ordovician instead of Carboniferous, as the Peshastin 

 is called by Smith and the Gunn Peak by Weaver. Nothing can 

 be said of the remainder of the Paleozoic history of the area. The 

 absence of later Paleozoic and Triassic seems to be general in the 

 region of the Cascade Mountains. In Jurassic time, however, 

 there was a notable period of deep-seated volcanic activity, result- 

 ing in the intrusion of the great Sierra Nevada- Cascade granodi- 

 orite batholith, possibly the greatest of igneous intrusions. 2 This 

 batholith is represented by two terranes in the Skykomish Basin. 

 The first is the Tye soda granite in the northeast, and the second 



X G. M. Dawson, Ann. Rcpt. Can. Geol. Surv., N.S., VII (1894), 37B-49B. 

 2 R. A. Daly, Igneous Rocks and Their Origin (1914), p. 53. 



