2g6 



University of California. 



[Vol. i. 



extinction are common. The olivine is more abundant, but in man- 

 ner of decay resembles that just described. The decomposition 

 products of this mineral have so penetrated the angular spaces, as 

 well as the feldspars themselves, that the presence of analcite was 

 not detected. Magnetite is very abundant, both as a primary con- 

 stituent and as secondary dust, in the olivine decomposition prod- 

 ucts. Opaque granules are numerous in the feldspar of one slide. 

 In another it is penetrated by minute clear rods, probably apatite. 



There is one type of the dark rocks of uncommon interest. 

 As usual the feldspar predominates, but it is comparatively fresh. 

 The augite is also fresh. The amount of serpentinous matter 

 showing the appearance of olivine decomposition is large. This 

 serpentinous substance has spread through the rock, almost iso- 

 lating individual feldspar crystals. It also appears in angular 

 spaces of various sizes, spaces which resemble those occupied by 

 analcite in the other specimens. Portions of these spaces not 

 filled with this green matty material are occupied by a clear sub- 

 stance in the form of aggregated individuals, showing the polari- 

 zation of calcite. Treated with dilute acid this is decomposed 

 with effervescence. Lying either in the green products, partially 

 in the calcite, or on the borders of the angular spaces, are spheru- 

 lites of a very peculiar character. (Plate 16, Fig. 6.) They gen- 

 erally possess a dark center, around which are placed wedge- 

 shaped plates to form an almost perfect sphere when not inter- 

 fered with. The outer contour of the spherulites is bordered by 

 a dark crenulate line, a short distance within which is another 

 crenulate circle formed of two lines. Under crossed nicols a dark 

 cross is seen, which even extends at times beyond the boundary 

 of the spherulite proper to radially arranged calcite individuals. 

 The spherulite itself has a very pale yellow color, while the car- 

 bonate is colorless. After treatment with hot concentrated sul- 

 phuric acid and staining with fuchsin, the centers and borders only 

 are seen to have been affected. The invariable position of the 

 spherulites and their association with calcite would indicate that 

 they were not formed primarily in a glassy portion of the rock, but 

 are secondary products partly replacing some easily decomposable 

 primary mineral (possibly one of the sodalite group). No known 



