NEOCENE BASINS OP THE KLAMATH MOUNTAINS 501 



Pitt river or the Sacramento, and it is maintained that its individuahty has been 

 kept ahnost unchanged to the present. As one of the larger streams of the region, 

 therefore, the Klamath is younger in age than either the Trinity or the Rogne river. 



AGE OF CERTAIN GRANITES IN THE KLAMATH MOUNTAINS 

 BY OSCAR H. HERSHEY* 



I Abstract'] 



Small batholites and dikes of granite, quartz-mica- diorite, and intermediate types 

 are shown to occur at various places in the Klamath region, but in areas quite sub- 

 ordinate in extent to those of the metamorphic rocks into which they have been 

 intruded. The same contains extensive areas of serpentine, and instances are given 

 of the granitic rocks having been intruded into the serpentine to prove that the 

 granites are newer, in accordance with the determined relations of these rock -types 

 in the vSierra Nevada region, and the reverse of the supposed relation between the 

 granite and the serpentine of tlie Coast ranges. 



The black slates of the Klamath region are divided into two distinct series, 

 referred to as the Lower slates and the Upper slates. The former are considered 

 Devono-Carboniferous in age, being in part equivalent to the Calaveras formation- 

 The latter are correlated, on the evidence of their lithology and of their structural 

 relations to the Lower slates and to a certain extrusive greenstone formation similar 

 to the diabase and porphyritic formation of the Sierra Nevada region, with the 

 Mariposa formation of late Jurassic age. The intrusion of granite occurred later 

 than the deposition of these Upper slates ; also it is shown that the granites are 

 much older than the Chico formation resting on them, as they had suffered nnich 

 erosion prior to the Chico epoch. 



It is finally concluded that the weight of evidence places the granitic intrusion 

 just about at the close of the Jurassic period. The effect of the argument is to show 

 that there is a sound basis for tiie inference heretofore entertained that the Klamath 

 mountains belong rather to the sierra Nevada system than to the Coast ranges and 

 may be considered a sort of outlier to the former. 



FELDSPAR-CORUNDUM ROCK FROM PLUMAS COUNTY, CALIFORNIA 



BY ANDREW C. LAWSON 



\_ Abstract'] 



Mr Turner, of the United States Geological Survey, has called attention to the 

 prevalence of feldspathic " albitic " dikes cutting serpentine in various parts of 

 the Sierra Nevada. The rock of which the present paper treats apparently be- 

 longs to this series of dikes. It occurs as a white, coarse grained dike cutting the 

 serpentine of the eastern flank of Spanish peak, Plumas county. The rock is com- 

 posed of 84 per cent of oligoclase and 10 per cent of corundum in crystals up to 

 over 2 inches in length, and rather irregularly distributed through the feldspathic 

 groundmass. 



The following is an analysis of the feldspar : 



SiO^, 6L36; AlA, 22.97; NaA 8.08; CaO, 5.38; H,0, 1.72. Total, 99.51; Sp. 

 cr., 2.63. 



* Presented by A. C. Lawson. 

 LXXI— Bull. Geol. Soc. Am.. Vol. 12, 1900 



