304 University of California Publications in Geology [Vol. 11 



of a dull color, yellow to gray, while the colors of the Franciscan 

 cherts are varied and brilliant, because of the large amounts of iron 

 and manganese oxides which they contain. 



In thin sections of the Franciscan cherts isotropic material is not 

 abundant, but it is quite common to find large amounts of isotropic 

 silica in the Monterey cherts. Although the Franciscan cherts are 

 largely recrystallized and contain little amorphous silica, the radio- 

 larian remains are still quite prominent. In the Monterey cherts 

 very few organic remains other than foraminifera are found. 



The lamination seen in the Monterey cherts, which is so character- 

 istic of them, is not so common in the Franciscan cherts. While lami- 

 nation does exist in some of the Franciscan cherts it is less pronounced, 

 and there is no sharp contrast, as a general thing, between the bands 

 of different material. They grade into each other almost imperr 

 ceptibly. In rare cases a rock may be found in the Franciscan cherts 

 which shows as strong banding as is found in the Monterey cherts. 



The Monterey cherts do not show the waxy luster and well devel- 

 oped conchoidal fracture shown by most of the Franciscan cherts, and 

 as a general thing they contain a larger amount of earthy material. 

 This statement meets exceptions in the case of the flinty cherts of the 

 Monterey. The Monterey cherts are less dense than the Franciscan 

 cherts. 



The difference in the nature of the two groups of cherts is reflected 

 in a comparison of the shales which are interbedded with them. In 

 the Monterey group the shales appear to be ordinary terrigenous 

 shales, while the shales of the Franciscan are unlike ordinary shales. 



In the Franciscan, the shales and cherts are not intercalated with 

 thin beds of sandstone. In the Monterey cherts there are numerous 

 beds of a peculiar type of sandstone in close association with the 

 bedded cherts. 



OCCURRENCES OF RADIOLARIAN ROCKS 



The following paragraphs will describe certain occurrences of 

 radiolarian rocks in other parts of the world. While the larger and 

 more important occurrences are summarized, no attempt is made at 

 completeness. 



Radiolarian remains are found in many types of sedimentary 

 rocks. Hill 30 in a summary of the literature treating of their occur- 



36 Hill, W., Rocks containing Radiolaria, Proc. Geol. Assoc., vol. 23, p. 62, 

 1912. 



