lawson.] Pluwiasite, an Oligoclase- Corundum Rock. 



229 



undetermined. There is no corundum discoverable in this facies 

 of the dyke. 



Correlation. — Turner has given us an account* of an extended 

 series of white feldspathic dykes distributed throughout the gold 

 belt of the Sierra Nevada, several of which occur in the vicinity 

 of Meadow Valley to the east of Spanish Peak. These rocks are 

 classed by Turner under the soda syenites, and as the feldspar in 

 those eases investigated by him consist almost wholly of albite, he 

 calls them albitites. The dyke with which we are concerned in 

 this paper evidently belongs to this series, although even in the 

 non-corundiferous facies it cannot be called an albitite. These 

 dykes according to the writer's observations vary considerably in 

 their mineralogical composition, some being rich in quartz and 

 others quite devoid of it, so that, although having a distinct 

 consanguinity, they would fall into a number of petrographically 

 different classes. Plumasite is the first of these in which 

 corundum has been found, but others having this character will 

 doubtless be found when the field is better known. 



* Notice of some Syenitic Rocks of California. Am. Geol., Vol. XVII, June, 

 1896, p. 375 et seq. 



University of California, 



April, 1903. 



