[8 



University of California. 



[Vol. 2. 



the exception of the greenish serpentinoid fragments, no other 

 material than that of volcanic origin. These beds are quite remark- 

 able in this respect, as well as in regard to the exceedingly fresh 

 condition of portions, and the beautiful symmetrical forms assumed 

 by the glass. 



Chemical Character. — An uncovered slide was digested for some 

 hours in a strong solution of caustic potash without producing any 

 apparent effect. A chemical analysis of a very compact specimen 

 gave the following composition : — 



SiO, 



ALA 



CaO 



MgO 



K,0 i 



Na,0 \ 



Ig 



74 



84I 



1 2 



577 





983 





262 



5 



360 



5 



273 



99 



296 



2 



402 



Total 

 Sp. gr. 



Save for the lack of iron, it will be seen that this ash closely 

 resembles in composition many acid rhyolites. Too little is yet 

 known of the geology of the Coast Ranges to enable us to say 

 whether the eruption to which the ash beds are due, can be corre- 

 lated with any of the acid volcanic rocks which are found in many 

 places. Other beds containing volcanic ash in the form of glassy 

 pumice, are known in the California Miocene, but nowhere else in 

 such thick beds, and so free from foreign material. 



KNOXVILLE BEDS. 



Occurrence. — The Knoxville appears at two points on the north- 

 ern slope of the Point Sal ridge. The larger area, which is nearly a 

 mile long, forms almost the whole of the upper portion of the valley 

 of Corralitos Creek lying east of the spheroidal basalt. The other 

 outcrop is much smaller, occurring in the same valley a half mile 

 below the lower dairy. The larger area extends up to within 100 

 feet of the summit of the ridge, reaching an elevation of 1,050 feet. 

 The character of the beds is identical with that of the Knoxville, 



