84 



University of California Publications. [Geology 



eral was erroneously determined as margarite by Eansome, but 

 a chemical analysis proves it to be muscovite. The analysis was 

 kindly made for the writer by E. S. Larsen, Jr., 



SiO 2 



48. 



.42 



APO 3 



28. 



41 



FeO 



2 



,10 



CaO 



0. 



48 



MgO 



3. 



.81 



Na 2 



1. 



95 



K 2 



10. 



36 



H 2 



4. 



72 





100. 



25 



The size of the optic angle varies. Most of the plates have a 

 large angle just within the field of the microscope, like ordinary 

 muscovite, while other plates show a considerably smaller angle, 

 perhaps between 50°-60°. It is quite possible that some of the 

 plates have a higher percentage of silica than others, which may 

 account for the smaller angle. 



The presence of muscovite instead of margarite is more in 

 accord with the observations of the other petrogra pliers pre- 

 viously mentioned who report muscovite as an associate, and also 

 with its occurrence elsewhere in the State. Epidote is quite sub- 

 ordinate in this mass ; consequently almost the whole of the lime 

 of the original rock has gone to the formation of lawsonite. The 

 large amount of muscovite indicates that the original rock con- 

 tained much potash feldspar, and in fact indications point to the 

 probability that the boulders rich in lawsonite are remnants of a 

 rock which was mineralogically different from the surrounding 

 soda-rich rocks. 



On the western slope of the Berkeley hills, north of Berkeley, 

 there are several outcrops of actinolitic, glaucophanitic, and 

 chloritic schists; and it was from this region that the new amphi- 

 bole crossite, described by Palache, 8 was found. About three 

 miles north of the town a chloritic boulder was found, resting 

 upon an outcrop of chloritic schist which was very thickly 

 charged with thin plates of lawsonite. The boulder presents a 

 very striking appearance, due to the thin edges of the lawsonite 

 standing out as bleached white ridges on the weathered surface 



s Bull. Dept. Geol. Univ. Calif., 1894, 1, 181-192. 



