Annual report of the United States Geological Survey to the Secretary of the Interior . PLATE XLIV. PLATE XLIV. A. Diorite-porphyry, No. 298 S. N., showing the idiomorphic tendency of the plagio- clase and hornblende. With the analyzer, X 45. P = plagioclase phenocrystswith decomposed interior and rim of fresh feldspar; A = brown smaller plagioclases of the grouudmass likewise have idiomorphic ten-dency, so that the rock has a nearly panidiomorphic structure. B. Quartz-diorite-porphyry, No. 298 S. N., view of part of the same section as the previous, the section being made from
Annual report of the United States Geological Survey to the Secretary of the Interior . PLATE XLIV. PLATE XLIV. A. Diorite-porphyry, No. 298 S. N., showing the idiomorphic tendency of the plagio- clase and hornblende. With the analyzer, X 45. P = plagioclase phenocrystswith decomposed interior and rim of fresh feldspar; A = brown smaller plagioclases of the grouudmass likewise have idiomorphic ten-dency, so that the rock has a nearly panidiomorphic structure. B. Quartz-diorite-porphyry, No. 298 S. N., view of part of the same section as the previous, the section being made from a chip taken at the contact of the twodikes. The microcrystalline nature of the quartz-feldspar groundmass isshown, and in this groundmass are embedded plagioclase phenocrysts. Withthe analyzer, X U. S. GEOLOGICAL SURVEY SEVENTEENTH ANNUAL REPORT PART I PL. XUV. B A. DIORITE PORPHYRY, NO. 298 S. N. £. QUARTZ-DIOR IT E-PORPHYRY, NO 298 S. N. PLATE XLV. PLATE XLV. A. Hornblende-pyroxene-andesite, No. 72 S. N., showing the porphyritic plagioclase with glass inclusions. P = augite grains. The microlitic glassy grouudmassillustrating the hyalopilitic structure of Rosenbusch is not brought out. Withthe analyzer, x 55. B. Diabase, No. 415 S. N., showing the wedges of hornblende between the lath- shaped feldspars, and illustrating imperfectly the diabase-granular structure,the chief feature of which is the lath-like development of the feldspars withlater metasilicates. With the analyzer, X U. S. GEOLOGICAL SURVEY SEVENTEENTH ANNUAL REPORT PART I PL. XLV
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