Regory.] TESCHENITES. 181 
•rains, with bays # and internal cavities often filled with biotite or its 
Iteration product. The aggregation of biotite and magnetite is 
oticeable in all the sections. The large amount of titanium given 
i the analysis suggests ilmenite, but the iron grains are readily picked 
p by the magnet. Apatite is thickly distributed through the rock 
1 long broken needles and well-formed crystals which penetrate the 
eldspars in particular very deeply. 
The biotite is a pale yellow-brown variety, pleochroic, with distinct 
leavage and regular or ragged border, and is found included by or 
rouped with the magnetite, or more rarely scattered through the 
action . It is found in various states of alteration, and stages can be 
raced from the yellow unaltered biotite to a deep-red, fibrous or corn- 
act serpentinous mineral. This alteration product appears somewhat 
ke the iddingsite found in the California teschenite 1 and quite com- 
ionly in basalts, but there is here no olivine represented by ciystal 
utline or characteristic parting, nor lines of alteration, as is the case 
i slides where the red mineral occurs as the undoubted secondary 
lineral after olivine, and therefore the presence of olivine is not 
turned. 
Augite is the most prominent rock constituent by reason of its 
evelopment into large, well-formed crystals and its beautiful violet- 
rown color and faint pleochroism. The prism sections, which are 
oout twice as long as broad, sometimes attain a length of half an inch 
id may have perfect crystal boundaries or broken, irregular edges, 
asal sections are generally almost sqware by slight development of 
rism faces, but show also rounded and rectangular outlines. In some 
)ecimens the violet augite has a light-green border of some regirine 
rpe of pyroxene, which is also occasionally present apart from the 
igite. The augites have altered along the cleavages to the same 
iddish mineral found replacing the biotite, and occasionally the crystal 
entirety replaced by a green chloritic mineral or by calcite, or may 
3 bordered by a zone of serpentine, often in radial bunches. 
The feldspars occur typically in long, broad laths or narrow, rod- 
ke bodies. They are nearly all striated and occasionally have Carls- 
ad twinning. The largest crystals are in the pink variety, and here, 
t in all types, alteration products prevent accurate determination in 
le majority of cases. However, sections are present in the slide 
hich have the albite and Carlsbad twins developed and are fresh and 
•ight in appearance. One such section was cut in the zone suited for 
)tical determination by the Michel Levy method, and gave the fol- 
wing measurements: Albite extinction, 13°; Carlsbad, 4°; the differ- 
ice is 8°, and by reference to the table is found to correspond to the 
i Bull. Geol. Dept. Univ. California, Vol. 1 and Vol. II. 
