410 W. H. MELVILLE CHEMISTRY OF THE MOUNT DIABLO ROCKS. 



calcareous shale d, and a peculiar rock e, whicli may be considered an un- 

 usual form of serpentine. The high percentage of alumina, however, gives 

 a ratio of basis to silica very different from that of serpentine. These analy- 

 ses are interesting in that they show the composition of the same species of 

 rocks, which have been previously discussed, in the extreme northwestern 

 part of the serpentine dike. 



The following analyses of shale a was made with a view of ascertaining 

 its mineral composition. Shale a will be found to contain albite, for the 

 final residue in the scheme below is almost identical with the composition of 

 this feldspar. The shale fuses to a brown-black glass, so also after the re- 

 moval of the carbonates, and the final residue fuses to a light-colored glass 

 at about the same number on the scale of fusibility. A slide of this rock 

 showed the presence of albite. Information as to the other constituents is 

 wanting. 



Analysis of Neocomian Shale. 



Kemoved by dilute hydrochloric acid (ascertained 



by difference) - 



Per cent 

 ___ 24.53 



Kemoved by strong hydrochloric acid: SiOg 



A1A-— 



0.03■ 

 6.02 







FeA ___ 



FeO 



MnO-__. 



6.00 

 0.40 

 trace 





_-. 16.88 



CaO 



0.58 







MgO____ 

 Na20-___ 

 K^O 



Kemoved by sodium carbonate solution : SiOj 



Final residue: SiOg 



3.17 



0.3G 



0.32, 



18.26_ 



27.77] 





_ _ 18.26 







AlA— - 

 FeA ___ 



8.00 

 0.41 







MnO-___ 

 CaO 



0.05 

 trace 





___ 40.33 



MgO 



Na^O..-. 



0.25 

 2.75 







K,0..__. 



1.10 







100.00 



Series V. — This series consists of two specimens from a locality at the 

 # head of Bagley creek in the metamorphic area, and represents the passage 

 of the common red shale into silicified shale or phthanite. The great mass 

 of these deposits in Mount Diablo is exceedingly folded and distorted, yet 

 shows the alternating layers of the two components, a phenomenon quite 

 usual in this class of rocks in the Coast ranges. This rock is very, friable, 



