BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 11, pp. 223-230 April 7, 1900 



TERTIARY GRANITE IN THE NORTHERN CASCADES* 



BY GEORGE OTIS SMITH AND WALTER C. MENDENHALL 



{Read before the Society December SO, 1899) 

 CONTENTS 



Page 



Introduction 223 



General geology 224 



Sedimentary rocks 224 



Volcanic rocks 225 



Plutonic rocks 225 



Distribution of the granite 226 



Areal extent 226 



Dikes 226 



Contact metamorphism. . 226 



Endomorphic phenomena 226 



Metamorphism of the sedimentary rocks 227 



Structure 228 



Sedimentary rocks . . .- 228 



• Nature of intrusion 228 



Resume 229 



Introduction 



The area to be discussed in this paper is in the immediate vicinity of 

 Snoqualmie pass in the northern Cascades. Snoqualmie pass is in central 

 Washington, about 10 miles north of where the Northern Pacific railroad 

 crosses the range. It is a low pass, less than 3,100 feet above sealevel, 

 and is the only point in the state where the range is crossed by a wagon 

 road. On all sides of the pass, however, rugged peaks rise to elevations 

 of from 5,700 to 6,300 feet. Although the geologist finds that this bold 

 topography prevents rapid progress, while the luxuriant vegetation of the 

 western slope at times presents almost impassable obstacles, yet the rock 

 exposures in the higher parts of the range are such as to furnish conclu- 

 sive evidence as to their character and relations. 



In the summer of 1895 Snoqualmie pass was visited by a United States 

 Geological Survey party under Mr Bailey Willis, with the senior author 



* Published by permission of the Director of the United States Geological Survey. 

 XXXIII— Bull. Geol. Soc. Am., Vol. 11, 1899 (223) 



