12 



University of California. 



[Vol. 2. 



knife, and breaks with a conchoidal fracture. The microscopic 

 slide showed numerous organic remains, as before described. It 

 contains no carbonates. It is interesting to note the close resem- 

 blance of this analysis to that given by Lawson and Posada,* of the 

 white bituminous shale at Monterey (II). Another analysis (III) 

 was made of an opaque flint; and (IV) is the percentage of silica in 

 a clear black flint. 



I. II. III. IV. 



86.92 86.89 92.37 98.1 

 4.27 2.32 2.46 not det. 

 1.28 " " 



Si0 2 

 ALA 

 Fe 2 3 

 CaO 

 MgO 

 K 2 

 Na 2 



Ig- 



Total 

 Sp. gr. 



1.60 

 trace 



• 2.48 

 5-13 



100.40 

 2.12 



i-43 

 trace 

 1.26 

 2.32 

 4.89 



99-39 

 1.8 to 2.1 



1.70 



274+CO, 



99.27 

 2.54 



2-57 



The organic remains in No. I, if they ever were calcareous, have had 

 the carbonate entirely replaced by silica. The following experiments 

 were carried on for the purpose of determining the nature of the 

 silica in these rocks, and whether the amorphous material in the 

 flint and shale was really colloid silica or an aggregate of minute 

 fragments of an acid volcanic glass. A gram of the white shale 

 was finely powdered and treated with a strong solution of caustic 

 potash for two days, with the result that all but 1 1 per cent of the 

 powder dissolved. An equal amount of powdered pumice was then 

 treated in the same manner, with the result that it lost a small frac- 

 tion of one per cent. This proves that the amorphous material in 

 these rocks is of the nature of opaline or colloid silica. A slide of 

 the chalcedonic flint treated with a solution of the alkali was not 

 affected. A specimen of the bituminous limestone which appeared 

 to consist almost wholly of minute organisms, yielded with a rough 

 test about 60 per cent of calcium carbonate, and 20 per cent of 



* Bull. Dept. Geol. Univ. Cal., Vol. I, p. 25. 



