150 arnold and anderson recent stream conglomerate 



Origin and Deposition of the Cement 



The serpentine and associated nietamorphic rocks of the ridge in 

 which White creelc heads are the source of the cement which hardens the 

 conglomerate. An analj'sis of similar serpentine from near the New 

 Idria quicksilver mine in the same general metamorphic area is given 

 below (A), and to this are added analyses of two other serpentines (B 

 and C) and a glaueophane schist (D) from the same formation, near 

 moimt Diablo, farther north in the range. 



Analyses of Serpentines and Glaueophane Schist firjjn the Diahlo Range, 



California^ 



A — Light green, marmolitic serpentine, New Idria, San Benito conuty, Cali- 

 fornia. W. H. Melville, analyst. (Loc. cit, p. 240.) 



B — Serpentine from near Arroyo del Cerro, Contra Costa county, California. 

 W. H. Melville, analyst. (Loc. cit, p. 250.) 



C — Friable serpentine from same locality as B. W. H. Melville, analyst. 

 (Loc. cit, p. 249.) 



u — ^Glaucopbane-scbist. Pine canyon. Mount Diablo, Contra Costa county, 

 California. W. H. Melville, analyst. (Loc. cit, p. 247.) 





A 



41.54 



2.48 



B 



C 



D 



SiOj 



34.84 



.42 



6.08 



1.85 



30.74 



7.02 



.42 



.07 



1.67 



15 . 72 



.04 



.68 



Trace. 



.01 



30.96 



.39 



■ 5.00 



2.34 



33.84 



3.81 



.34 



.14 



2.16 



14.02 



.02 



.78 



Trace. 



.09 



47.84 



A1,,0, 



16.88 



Fe.,0, 



4 99 



FeO 



1.37 

 40.42 



5.56 



MgO 



7 89 



CaO 



11.15 



Na^O 





3.20 



K,0 





.46 



H2O at 100° 



14.18 



.17 



HjO above 100° 



1 81 



P2O5 





14 



Cr,0, 







NiO 



.04 





:\rnO 



.56 











100.03 



99.56 



99.89 



100.65 



An analysis by Dr E. C. Sullivan shows that the cement deposited on 

 "\Aniite creek is made up principally of calcium and magnesium carbon- 

 ates, with minor amounts of silica and ferric oxide. A comparison of 

 this anal3^sis with that of the serpentine (A) from the general area in 

 ■which White creek heads makes obvious the origin of the magnesium in 



■ F. W. Clarke : U. S. Geological Survey Bulletiu no. 22S, 1904, pp. 246, 247, 249, 250. 



