The geology of Ascutney Mountain, Vermont . /. Titanite is here moreabundant, and explains the somewhat higher percentage of TiO^ inthe analysis. The higher MgO is ascribed to the more abundantbiotite. The rock shows no indications of crushing; we can not, therefore,attribute the porphyritic structure to cataclastic processes. Thegroundmass has unquestionably crystallized in its present form froman igneous magma. The order of crystallization of its componentminerals is the same as in the green rock. Several facts favor theview that the feldspar phenocrysts belong to an earlier stage in thecrys
The geology of Ascutney Mountain, Vermont . /. Titanite is here moreabundant, and explains the somewhat higher percentage of TiO^ inthe analysis. The higher MgO is ascribed to the more abundantbiotite. The rock shows no indications of crushing; we can not, therefore,attribute the porphyritic structure to cataclastic processes. Thegroundmass has unquestionably crystallized in its present form froman igneous magma. The order of crystallization of its componentminerals is the same as in the green rock. Several facts favor theview that the feldspar phenocrysts belong to an earlier stage in thecrystallization than that which produced the groundmass. PLATE V. A, Segregation of mica and hornblende concentrically arranged, in paisanite(the same section of the segregation also appears in the lower right-hand quad-rant of the micrograph represented in PI. IV, B); ordinary light, X 24. (See p. 73.) B, Basic segregations in nordmarkite at Crystal Cascade; one-half natural size.(Seep. 64.) 62 U. S. GEOLOGICAL SURVEY BULLETIN NO. 209, PL. V. m; H <^
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