278 University of California Publications in Geology [Vol. 11 



of the hydrated sodium aluminum silicate, natrolite. This is associ- 

 ated with albite and other soda-rich minerals. In these veins the 

 mineral benitoite, BaTi(Si0 3 ) 3 , occurs. Neptunite [(Na.K 2 (Fe, Mn) 

 (Si, Ti) g 12 )] is also abundant. The natrolite veinlets and the 

 associated minerals appear to be produced by the contact action 

 of the peridolite magma. While the occurrence of natrolite and 

 neptunite at this locality seems to be a unique occurrence, albite is a 

 very common mineral in the Franciscan schists, often occurring in 

 the form of veins. 



In view of the foregoing facts, it would appear highly probable 

 that, while a part of the alkali content of the glaucophane schists may 

 have been originally present, there has also been a notable contribu- 

 tion of alkalies from some external source. 



THE OCCURRENCE OF BEDDED CHERTS IN THE 

 MONTEREY GROUP 



There are other formations in the California Coast Ranges which 

 contain banded cherts and shales. Of these the most important is the 

 Monterey group of middle Miocene age, the cherts of which in some 

 respects are similar to those of the Franciscan group. On account of 

 this similarity, the Monterey cherts were studied in the hope that a 

 comparison would throw some light upon the origin of the Franciscan 

 cherts. The cherts of the Monterey group, as well as the bedded cherts 

 of other horizons to be mentioned later, differ from the Franciscan 

 cherts in that they contain no radiolarian remains. 



Lithologic Types in the Monterey Group 

 The assemblage of strata in the Monterey group comprises several 

 lithologic types : diatomaeeous earth, diatomaceous shale, ordinary 

 terrigenous shale, bituminous shale, "white shale," cherts of various 

 sorts, limestones, sandstones, and tuffs. Various admixtures of diato- 

 maceous earth with sand and volcanic ash are known. Associated 

 with these, there are various extrusive and intrusive igneous rocks. 

 The various members of this formation have been described in numer- 

 ous publications. 21 



21 Lawson, A. C, The Geology of Carmelo Bay, Univ. Calif. Publ., Bull. Dept. 

 Geol., vol. 1, p. 1, 1893. 



Arnold and Anderson, Geology and Oil Besourees of the Santa Maria Oil Dis- 

 trict, U. S. Geol. Surv. Bull. 322, 1907. 



Lawson and Palaehe, Geology of the Berkeley Hills, Univ. Calif. Publ., Bull. 

 Dept. Geol., vol. 2, p. 349, 1901. 



Lawson, San Francisco Folio, op. cit. 



