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University of California. 



[Vol. i. 



refraction strong and negative. The interference figure is biaxial, 

 and hence the crystals are orthorhombic. Warm concentrated 

 hydrochloric acid failed to gelatinize it, so that it is probably not a 

 zeolite. In all respects except the absence of cleavage the min- 

 eral corresponds closely to a colorless anthophyllite, and it is so 

 regarded provisionally. 



It is this phase of the rock which exhibits locally the schistose 

 structure before mentioned. In thin sections this structure is 

 expressed by a more or less perfect parallelism of the longer axes 

 of the mineral grains composing the rock. Very little shattering 

 or crushing of the grains was observed, but the banded structure 

 was quite noticeable. 



A variety of this type was observed in which the essential con- 

 stituents are the same as, but the structure is quite different from, 

 that of the type. The structure is ophitic, the lath-shaped feldspars 

 interlacing to form a network filled in with allotriomorphic horn- 

 blende. There is also present as an accessory constituent in addi- 

 tion to magnetite, ilmenite in grains and crystals, well marked by 

 its dark color, rhombohedral cleavage, and border of gray leucox- 

 ene. The variety thus presents the characteristic appearance of a 

 diabase, in which, however, hornblende takes the place of augite. 



The second type presents in thin sections a coarse ophitic to 

 granular structure, thus differing from the first type, from which it 

 also differs in the presence, in addition to feldspar and hornblende, 

 of both orthorhombic and monoclinic pyroxene. The feldspar is 

 for the most part in long and short prismatic crystals, idiomorphic, 

 and with abundant polysynthetic twinning striations of plagioclase. 

 Examined in the same manner as before described, it gave extinc- 

 tion angles uniformly larger than did the feldspar of the first type. 

 The maximum angle was 29 , the average 27 , which indicates its 

 place near the middle of the labradorite series. The general appear- 

 ance of the feldspar with regard to inclusions and alteration is simi- 

 lar to that of the first type described. In some crystals, however, 

 particularly where the feldspar is in contact with pyroxene, the 

 feldspar is charged with needles of a pale greenish or colorless min- 

 eral, apparently secondary, the exact nature of which was not 

 determined. 



