1918] Davis: The Radiolarian Cherts of the Franciscan Group 269 



The extremely high silica and the important amounts of iron are 

 the most notable features. No determination of titanium was at- 

 tempted in analyses n and in. Qualitative examination of a number 

 of typical specimens of red chert showed, however, that there was not 

 enough titanium present to give a reaction on boiling with tin in 

 hydrochloric acid after fusion with sodium carbonate. 



The following are analyses of Franciscan shales interbedded with 

 the cherts, together with an analysis of a soft gray shale parting from 

 the cherts of the Lower Culm in England, and an analysis of average 

 shale according to Clarke : 



I. Analysis of a brownish red shale from the red cherts of Bagley Canon, 

 Mount Diablo. Melville, op. cit. 

 II. Partial analysis of red shale from Point Richmond. 



III. Partial analysis of red shale from Eed Rock Island. 



IV. Partial analysis of green shale from Kock Ridge Quarry, Oakland. 



V. Partial analysis of red shale collected at end of Twenty-fourth and 

 Hoffman street car line, San Francisco. 

 VI. Soft red shale from Red Kock Island, once mined as paint rock. Analy- 

 sis by Irving Miller, given by Lawson in San Francisco Folio, op. cit. 

 VII. Analysis of soft gray shale parting from radiolarian rocks of Lower 

 Culm. Hinde and Fox, Quar. Jour. Geol. Soc, vol. 51, p. 629, 1805. 

 VIII. Percentages of principal elements in Clarke 's composite analysis of 78 

 ordinary shales: Data of Geochemistry, U. S. Geol. Surv. Bull. 616, 

 p. 28, 1916. 

 T II III IV V VI 

 SiO, 69.98 68.22 63.47 62.35 57.55 50.58 



Ti(),. 55 



P 2 5 .05 



ALO., 11.69 11.31 10.14 15.45 15.65 14.35 

 Fe 2 0, 6.23 8.75 14.60 4.95 11.85 15.64 



FeO 1.08 70 65 



MnO .49 .13 .08 .55 1.20 .36 



CaO .38 .99 .74 2.05 1.65 1.77 



MgO 1.29 2.39 2.41 3.05 2.50 3.08 



Na 2 3.72 70 



K,0 .73 3.84 



H 2 (a) 



110°C 1.03 1.39 1.44 1.75 2.40 3.30 

 H 2 on 



ignition 2.92 4.42 3.91 4.45 4.10 5.19 



Soluble 38 



VII 



VIII 



67.8 



58.38 





.65 





.17 



19.8 



15.47 



1.4 



4.03 



.4 



2.46 





trace 





3.12 



1.2 



2.45 





1.31 



4.8 



3.25 



.9 



1.34 



3.6 



3.68 



99.59 97.60 96.79 95.30 96.90 100.39 99.9 2.64 CO. 



.65 SO., 



.05 BaO 



.81 C, organic 



100.46 



