INTRUSIVE SHEETS IN MOUNT EVERTS. 85 



be andesine-labradorite with, marked zonal structure, and with cracking- and 

 secondary inclusions similar to those in the andesite-porphyries of this 

 region. The quartz crystals are sometimes idiomorphic pyramids, or are 

 nearly spherical, or are irregularly shaped. They contain bays and 

 inclusions of groundmass and many liquid inclusions with cubes and gas 

 bubbles; rhombohedral cleavage is occasionally developed. The hornblende 

 is green and more or less chloritized. A few crystals of biotite and of 

 sphene were noticed. Magnetite occurs in small individuals, and colorless 

 apatite in comparatively large ones. Allanite is present in brown pleochroic 

 crystals, with idiomorphic form and zonal structure. Strongly pleochroic 

 epidote in irregular grains is sparingly present as a secondary mineral. 

 The groundmass is fine grained, microgranular, with minute idiomorphic 

 quartzes and abundant crystals of magnetite (168, 169). 



INTRUSIVE SHEETS EST MOUNT EVERTS. 



There are a number of intruded sheets of igneous rock within the 

 Cretaceous strata of Mount Everts, the lowest being exposed near the base 

 of the south side of the mountain, and the highest at the top of the west 

 escarpment. The rocks as a group are dark greenish and brownish grays 

 to slate color. They are dense and aphanitic to very fine grained, and for 

 the most part are free from prominent phenocrysts. The rocks are altered 

 holocrystalline andesites and andesite-porphyries. 



The coarsest-grained form occurs in a sheet 20 to 30 feet thick at the 

 base of the south face of the mountain (365). The rock is greatly fractured, 

 with joints along which there has been sliding about parallel to the bedding 

 of the inclosing sedimentary strata. It consists of nearly idiomorphic lime- 

 soda feldspars, with low extinction angles and low double refraction, about 

 0.4 mm. long, the marginal part being unstriated and cloudy. A few are 

 phenocrysts 2 mm. long. There is considerable serpentine and a little pale- 

 green augite not yet altered. Magnetite occurs in small crystals, and 

 colorless apatite is abundant in minute thin prisms. Numerous shreds of 

 red-brown biotite may be secondary. The rock is a pyroxene- andesite- 

 porphyry. 



In the west escarpment several thin sheets were observed by Mr. 

 Wright. They are aphanitic and porphyritic (356, 357), with phenocrysts 

 of feldspar and decomposed pyroxene. The feldspar is partly altered, and 

 is probably labradorite. The groundmass is extremely fine grained and is 



