'Fairbanks. J 



Geology of Point Sal. 



63 



II. 



Feldspar, olivine, augite (with or without 



hornblende). 

 Feldspar, olivine, augite, hypersthene (with 



or without hornblende). 

 Feldspar, olivine, hypersthene. 

 Feldspar, olivine. 



III. 



Olivine, diallage, hypersthene, little feldspar, 



Olivine, diallage, hornblende, little feldspar. 



01ivine ; hypersthene, little feldspar. 



Olivine, augite or diallage, little feldspar. 



Olivine, enstatite, diallage. 



Olivine, hornblende. 



Olivine, diallage. 



Olivine. 



Diallaare. 



Olivine gabbro. 



1 



Olivine norite-gabbro. 

 Olivine norite. 

 Troctolite. 



Feldspathic lherzolite. 

 Hornblende picrite. 

 Feldspathic saxonite. 

 Picrite. 

 Lherzolite. 



Wherlite. 



Dunite. 



Pyroxenite. 



The feldspar of these rocks, with rare exceptions, all belongs to 

 anorthite. One exception is that of feldspar intergrown with quartz 

 in veins in the serpentine which seems to lie between labradorite 

 and albite. Feldspar approximating labradorite is found in several 

 of the diabasic dikes, but in all the facies of the gabbro it undoubt- 

 edly belongs at the extreme basic end of the series. Large extinc- 

 tion angles were noted, while the specific gravity ranges between 

 2.73 and 2.758. It is generally very fresh and free from inclusions. 

 In the rocks rich in olivine, alteration has begun, and where the feld- 

 spar forms but a small portion of the rock, as in certain facies of 

 the peridotites, it is completely altered to a white, opaque, and com- 

 pletely amorphous substance. In none of the specimens did apatite 

 appear as inclusions, either in the feldspar or any other of the com- 

 ponents. Twinning was noted in the feldspars on the carlsbad, 

 albite, and pericline laws, that of the albite prevailing. 



The monoclinic pyroxene has a uniform character, aside from 

 secondary changes, in all parts of the eruptive mass. In the hand 

 specimen it appears a deep green color, but in thin section under 

 the microscope it is non-pleochroic and almost colorless. In many 



