60 Hershey — Some Western Klamath Stratigraphy. 



The peculiar bluish bedded cherts occur throughout the area 

 of outcrop of this series, but in some localities are more 

 strongly developed than in others. They are especially promi- 

 nent south of the Black Bear mine, where I estimate the thick- 

 ness of the formation to be about 5000 feet, of which probably 

 3000 feet is chert. 



Beginning at the Orleans fault, two miles east of Orleans, 

 and proceeding thence up the valley of Pearch Creek, climbing 

 the western flank of Orleans Mountain, we find first a belt of 

 quartz schist (produced, by the shearing of chert) and asso- 

 ciated with it lentils of limestone, the whole dipping easterly 

 45° to 60°. This is succeeded by ordinary cherts and shales in 

 alternating layers, all dipping eastward at angles not less than 

 30°. But the formation has been very thoroughly shattered 

 by the intrusion of igneous material. In places, this occurs 

 in a network of small dikes traversing the sedimentary rocks 

 in all directions ; in others it is in large masses almost exclud- 

 ing the shales and cherts. Inclusions of the latter are exceed- 

 ingly common and vary in size from infinitesimal fragments to 

 masses a quarter of a mile in length. All the larger fragments 

 more or less preserve the original easterly dip. By means of 

 them one can trace, in Pearch Creek valley, the outlines of a 

 succession of strata at least 3000 feet thick, everywhere dip- 

 ping easterly at a comparatively steep angle. 



This thorough intrusion of the Blue Chert series by appar- 

 ently dioritic and diabasic material is general throughout its 

 extensive outcrop areas in the western Klamath region. Prob- 

 ably no quarter section of it is without these dikes and in 

 many square miles there is much more igneous than sedi- 

 mentary rock. I want to strongly impress the fact that this 

 intrusion is not local. 



In Pearch Creek valley, the intruded igneous material 

 appears to pass upward into a volcauic series of andesites and 

 rhyolites, which, if I rightly remember, is 800 to 1200 feet 

 thick. An important member in the lower part of the series 

 is an andesite characterized by small block-like crystals of 

 hornblende probably originally a pyroxene. This maj^ be 

 partly in the form of large dikes penetrating deep into the 

 complex of sedimentary and intruded rocks, but it also spreads 

 out in the form of a thick sheet. The upper portion of the 

 series consists of gently clipping beds of white rhyolite, some 

 of which is fragmental, suggesting tuffs. Specimens of dif- 

 ferent phases were submitted to Mr. Diller for microscopic 

 examination and he conceded the probability of this being a 

 volcanic series. Certainly its attitude and texture oppose the 

 idea of its having been intruded beneath the great thickness of 

 sedimentary rocks above it. 



