408 W. H. MELVILLE — CHEMISTRY OP THE MOUNT DIABLO ROCKS. 



white substance proved to be a carbonate and silicate of lime and alumina, 

 probably clay and calcite. 



h. Shale, very friable, occurring in small lumps about the size of a pea ; 

 the lumps were separated by calcite seams more abundant than in a, which 

 were removed in great measure before the analysis was made. 



c. Friable serpentine, apparently difFeriug greatly from true serpentine. 



d. A fair specimen of serpentine. 



Series III— Analyses of Specltnens from Arroyo del Cerro. 



(220) (221) (222) (223) 



a (2) a{V) b c d 



H^OatlOO^C 1.44 3.41 9.19 2.16 1.67 



H2O above 100° C 2.86 5.84 6.73 14.02 15.72 



SiOa 25.05 56.52 40.17 36.96 34.84 



P2O5 0.08 0.11 0.08 0.02 0.04 



CO2 24.20 little 3.48 



01-203 0.78 0.68 



A1203 8.28 17.65 12.76 0.39 0.42 



Fe203 0.27 1.58 2.10 5.00 6.08 



FeO 2.41 5.25 3.56 2.34 1.85 



NiO trace trace trace trace trace 



MnO 4.11 0.32 0.16 0.09 0.01 



CaO 27.87 1.09 4.24 3.81 7.02 



MgO 2.61 3.97 15.42 33.84 30.74 



Na20 undet. 2.14 0.57 0.34 0.42 



K2O undet. 2.36 1.36 0.14 0.07 



99.18 100.24 99.82 99.89 99.56 



The same processes of leaching and substitution which are discussed in 

 series II appear to have acted at the contact h. The shale h still possesses 

 all the characters of a true shale. Its composition shows a great increase 

 of water and magnesia, the latter by no means to be accounted for as car- 

 bonate, while there is a large decrease in silica and a small loss in alumina. 

 There has also been a later secondary action of surface waters or mineral 

 springs by which calcite and clay have resulted. Mineral springs similar 

 to those in Bagley canon might have existed formerly, but there is no indi- 

 cation of their existence at present. 



Series IV. — To the east of the Arroyo del Cerro are found the fossils 

 Belemnites and Aucella. This region comprises a portion of the metamorphic 

 area, and in it there is a good exposure of strata of shale and serpentine 

 which extends for about a hundred feet. A series of typical specimens were 

 collected from points in this exposure a few feet apart, of which the analyses 

 are ffiven below. 



