(JEOLOGY OF BAJA CALIFORNIA. 33 



The color of the rays vibrating- perpendicularly to oP, or 

 parallel to a, observed on foils, imbedded 'in more or less 

 vertical position in Canada balsam does not vary greatlv 

 from those parallel to C; the scheme of absorption 

 w^ould be b>a=^c. In convergent light it is noticed that 

 the angle of the optical axes is quite large, probably 

 nearer 20 ' than 10°, and that the plane of the optical axes 

 lies perpendicularly to the plane of symmetry, not as in 

 biotite, parallel to it. The mineral, therefore, belongs to 

 the micas of the " first-class," and is probably an Anoniitc. 

 Twins are common among the mica crystals, as evidenced 

 by the fact that apparently single foils between crossed 

 nicols prove to be made up of two or more, turned at a 

 certain angle with reference to each other. 



A basalt very similar to this, and also containing ano- 

 mite crystals in its cavities, has been described by L. 

 Bucca from Italy.* As a rule micaceous feldspar 

 basalts are very rare. 



*I1 monte de Roccamonfina, l^ott. Com. Geo). Roma, 1886, Nos. 7 and 8. 

 2d Ser., V(U.. in. ( 4) April 10, 1890. 



