86 H. W. FAIRBANKS — GEOLOGY OF THE COAST RANGES. 



form character, specimens from different portions of the Coast ranges dif- 

 fering more in deojree of metamorphism than in any original character. 

 Quartz is always present in more or less angular grains, but in all the 

 sections examined it is excelled in quantity by the feldspar. The feld- 

 spar consists partly of twinned plagioclase and partly of orthoclase, the 

 latter more abundant. Much of it, especially the smaller grains, is com- 

 pletely clouded. Hornblende was observed in only one specimen, that 

 from Del Norte county. Mica is occasionally present in irregular brown 

 scales, in part seeming to be of clastic origin and in part certainly as a 

 secondary mineral developed in the metamorphism. Small quantities 

 of iron oxide and other almost opaque minerals are present. The ab- 

 sence of hornblende from the sandstones of the central Coast ranges is 

 strong evidence in support of the view of their having been derived from 

 the preexisting granite axis in that region, the rare occurrence of horn- 

 blende in the granite of the Coast ranges (excepting that of the Klamath 

 mountains) being in such marked contrast to that of the Sierra Nevada. 

 The prevailing color on a fresh surface is a dark gray ; on weathering it 

 turns yellowish. The somewhat angular form of the grains is a notice- 

 able feature, one which bears out the view of the direct derivation of the 

 components from the crystalline rocks without a great deal of attrition. 

 The sandstones have been fractured and penetrated by silicious waters 

 in a somewhat less degree than the jaspers. A massive, thick bedded 

 character is to be noted in many places. These portions, though frac- 

 tured, do not show the effects of crushing, as do the shales and thin 

 bedded jaspers. 



Shale and Slate. — Shale and slate form, next to sandstone, the most 

 extensive portion of the series. Real slate, however, is not common on 

 account of the peculiar conditions which have existed. There are but 

 few areas of any extent where the pre-Cretaceous rocks appear in which 

 there is not to be observed the effects of extreme dynamic action as a crush- 

 ing force. These effects are particularly noticeable in the argillaceous 

 portion. So far as observed, the main cleavage is parallel to the sedi- 

 mentation. In areas where the pressure has been exerted normal to the 

 plane of sedimentation a fine cleavable slate has been produced, but 

 generally the strike and dip are so variable that a uniform direction of 

 pressure would seldom be normal to the bedding. Asa result, there are 

 two or more intersecting lines of cleavage, so that the rock breaks up into 

 sharply angular fragments. The action of numerous eruptive masses 

 as well as faulting have also had a very important influence in destroy- 

 ing the regular cleavage. Where the distortion has been greatest the re- 

 sult is a clay, which has acted as a sort of cushion for the less yielding 

 rocks. There are considerable areas of this series in the Coast ranges 



