568 WARREN S. SMITH 



Miocene, in accordance with Smith's interpretation. 1 The only 

 metamorphic effects experienced by this rock are the slight clouding 

 of feldspars and the formation of a system of joints. There is a 

 southernmost corner of another batholith, or, more likely, of a 

 subjacently connected continuation of the same batholith, north 

 of Grotto, and it is probable that these Tertiary batholiths form 

 the core of the Cascade Range throughout the northern half of 

 the state. Daly has correlated several of his batholiths with the 

 Snoqualmie batholith. 



PLIOCENE 



There is no stratigraphic evidence of Pliocene history. It is 

 physiographic rather. We infer that the Snoqualmie batholith 

 had a cover in excess of 2,000 feet in thickness. This cover was 

 removed and the entire area reduced to one of low relief in late 

 Miocene and post-Miocene time. In the Pliocene the area was 

 uplifted with a broad arch of north-south trend and with certain 

 minor warpings of transverse trend. Subsequent to this uplift, 

 but still in the Pliocene, the area was maturely dissected by steam 

 action. This process of peneplanation, uplift, and mature dissection 

 is evidence of the very considerable duration of the Pliocene. 



PLEISTOCENE 



This is the age of glacial occupancy, when glaciers of the alpine 

 type rilled the valleys to a depth of several thousand feet and 

 flowed down to their confluence with the Piedmont glacier of 

 Puget Sound. Evidence has been put forward by many writers of 

 two periods of glacial advance in the Puget Sound Basin, but 

 of course the last alpine glacier to occupy the valley would have 

 destroyed all evidence of any previous glaciation, and it can only 

 be said that the Skykomish Basin was maturely dissected by 

 glaciers of the alpine type in Pleistocene time. Comparatively 

 little time has elapsed since the glaciers withdrew from tlj£ valley. 

 The only stratigraphic evidence of this period is the accumulation 

 to a depth of several inches of a volcanic ash which has only a 



1 G. O. Smith and W. C. Mendenhall, "Tertiary Granite in the Northern Cas- 

 cades," Bull. Ccol. Soc. Am., II (1900), 201-28. 



