268 



University of California Ptiblications in Geology [Vol. 11 



In this shale there are a number of white horny fragments. In 

 their form they somewhat resemble fish teeth, but their exact nature 

 is not certain. Their outer surfaces possess a high luster like ivory, 

 and they are unaffected by acids. 



In the quarry in Piedmont, just across from the cemetery, a thick- 

 ness of several feet of similar shale is found near the base of the chert. 

 This contains the same toothlike fragments, and also contains certain 

 rounded white flakes of uncertain nature which may possibly be fish 

 scales. Thin sections of these shales show certain fragments with 

 peculiar structures which represent sections of the forms just men- 

 tioned. 



Analyses op Franciscan Cherts and Shales 

 The following tabulation gives the results of analyses of Fran- 

 ciscan cherts, together with the analyses of cherts from other localities : 



J. Brownish red chert from Bagley Canon, Mount Diablo. Melville, Bull. 

 Geol. Soc. Am., vol. 2, p. 411, 1891. 

 II. Siliceous red chert from Bed Bock Island. 



III. Siliceous red chert from Boint Richmond. 



IV. Hard, dark chert from radiolarian rocks of the Lower Culm measures. 



Hinde and Fox, Quar. Jour. Geol. Soc, vol. 51, p. 629, 1895. 

 V. Analysis of a dark, nearly black, chert from southern Scotland. The 

 Silurian Rocks of Britain. I, Scotland, Mem. Geol. Surv. United King- 

 dom, p. 641, 1899. 



VI. A milk white hornstone from Central Borneo. Molengraaff, Explorations 

 • in Central Borneo, p. 194, Leyden, 1902. 

 VII. A Tcieselschiefer from the Hartz Mountains. Caddell, Froc. Roy. Fhys. Soc. 

 Edin., vol. 8, p. 217, 1884. 







I 



II 



III 



IV 



V 



VI 



VII 



SiO, 





93.54 



95.08 



96.37 



87.3 



91.3 



97.19 



92.48 



ALA 





2.26 



2.17 



2.38 



5.7 



3.3 



1.45 



2.54 



Fe 2 3 





.48 



2.82 



1.70 



1.3 



.7 



1.12 



.55 



FeO 





.79 







1.4 



1.4 





.70 



MnO 





.23 















CaO 





.09 







.3 



trace 



.05 



1.36 



MgO 





.66 







1.2 



.8 



trace 



.32 



K,0 

 Na,0 





.51 

 .37 







.7 



.6} 



■A 



1.15 j 



.54 

 .54 



Loss ( 

 Loss 



S110°C .21} 

 on ignition .72^ 







1.9 



J 



.06) 

 .28f 



1.75 







99.86 



100.07 



100.45 



99.8 



99.2 



101.30 



100.78 



