ITS CONTRIBUTIONS TO THE GEOLOGY OF MAINK. [bull.1 
andesine. The feldspars of the groundmass are long, narrow, poor 
bounded individuals, nearly all striated, with an extinction nearly pa 
allel. ami hence olisjoclase. Colorless auffite is scattered thick; 
through the slide, commonly as grains, but also as prisms and has 
sections, and these occasionally extinguish in common, thus suggestii 
the ophitic structure. In places the feldspar microlites have son 
tendency to a spherulitic structure. Chlorite and iron are abundai 
in specks and patches, and calcite and quartz, together or separate!; 
occupy the cracks in the rock. 
The included jaspers are too dense to show structure and are off* 
partly surrounded by material composed of fragments of arkos 
feldspar, and quartz grains, set in a tine groundmass of similar materia 
This would indicate that the jasper was alread} T part of a conglon 
crate when fragments were removed by the igneous intrusion. It 
possible, however, that the presence of the arkose is due to secondai 
processes. 
CLASSY TYPE. 
The glassy type appears in the hand specimen as an exceeding] 
dense, blue-black rock with a dull luster and without the ordinal 
characteristics of vitreous material. Occasionally a small dot of i\ 
jasper is visible, but no other structures or minerals can be seen. Tl 
rock is very tough, and where struck with a hammer is reduced to 
powder of a lavender-gray color. Slickensides along the intersectin 
cleavages show movement since the mass has been in place. 
A thin section examined under the microscope revealed no minera 
present except a few rounded augite grains and some serpentine till in 
cracks, but it showed a groundmass composed entirely of very minuti 
feathery 7 fragments of some material which was not resolvable under tl 
highest powers. These featheiy structures are so arranged ahoi 
centers as to form round or elliptical spherulitic aggregates. Dire* 
evidence as to the nature of this groundmass is wanting, hut that it 
glassy and formed by sudden cooling seems evident. Whether tl 
spherulitic structure is secondaiy or primary, or, if secondary, whs 
its former nature was, is doubtful. The suggestion is made that 
may have been formerly a perlite reduced to its present condition b 
devitrification. A few glass} 7 spheres remaining in one place hear 01 
this supposition. The whole slide is densely sprinkled with chlorit 
and iron dust, thus bearing testimony to the basic character which tfc 
analysis brings out so clearly. 
Analysis. — The following analysis (I) by Dr. W. F. Hillebrand, of th 
United States Geological Surve} 7 , was made from the freshest materii 
obtained. Analysis II is inserted for comparison. 
