10 R. Arnold — Rocks from the Sawtooth Range. 



Camp between 1 and 2 miles southeast of Camp Black and 

 White, and a few others from the region adjoining the camps. 



General Geology. 



According to Mr. Stanard, the crest of the southwest end of 

 the ridge is composed of a coarse conglomerate striking parallel 

 with the range. The conglomerate has been subjected to 

 severe crushing and faulting, and quartz veins are not uncom- 

 mon in it. The rest of the country rock consists of alternating 

 hard sandstone, shale and slate, striking north and south and usu- 

 ally standing vertical. These rocks have been much fractured 

 and faulted and intruded by dikes of basic igneous rocks which 

 locally have produced garnetiferous and other schists. Quartz 

 veins carrying copper ores in commercial quantities occur along 

 the contact between some of these igneous dikes and the 

 intruded sedimentaries. The rocks adjacent to the veins are 

 also usually more or less mineralized. The age of the rocks is 

 unknown, but they may be a part of the series of conglomerate, 

 quartzite, diabase and serpentine that is exposed on the coast 

 between Cape Flattery and Grays Harbor at the western end 

 of the Olympics, and which has been described by the writer* 

 as of supposed pre-Cretaceous age. The occurrence of these 

 similar series of rocks at both the eastern and western ends of 

 the Olympics leads to the conclusion that the older formations, 

 at least, are dominated by east and west strikes, and, therefore, 

 that the Olympic Mountains, geologically speaking, must be 

 considered as an east-west range instead of a quaquaversal. 



Sedimentary Rocks. 



The country rock of the northwestern flank of the Sawtooth 

 Range consists of hard semi-metamorphosed sandstone and 

 shale occurring in alternating beds from a few inches to many 

 feet in thickness. These rocks stand practically vertical and 

 have in general a north and south or northeast-southwest 

 strike. 



The sandstone, which might properly be called indurated 

 arkose but hardly a quartzite, is fine-grained and in color dark 

 gray, and fractures with a rough surface. The rock is trav- 

 ersed by at least one system of parallel joint planes, in addition 

 to cleavage parallel to the bedding. Numerous small mica 

 flakes glisten on the surface in reflected light. In thin slides 

 the rock is seen to consist very largely of cherty quartz grains, 

 a little plagioclase feldspar and numerous flakes of brown and 

 white mica, mostly the latter. 



The hardened shale, or slate, as it is more commonly called, 

 is nearly black, cleaves quite easily and exhibits iridescent 



* Bull. Geol. Soc. Amer., vol. xvii, p. 459. 



