New York State Museum bulletin . in, North Creek and Lake Pleasant quadranglesmapped by the writer in the southeastern Adirondack region. The small area of granite .porphyry occupies about one-quarterof a square mile in the vicinity of the Indian lake Some ofthe rock has been used in the construction of the dam. There aremany good exposures, the best being at the dam and in the quarriesjust east. Where fresh the rock is greenish gray, and whereweathered it is pinkish. The rock is always coarse grained andrather gneissoid with the porphyritic texture usually well developedthough at times
New York State Museum bulletin . in, North Creek and Lake Pleasant quadranglesmapped by the writer in the southeastern Adirondack region. The small area of granite .porphyry occupies about one-quarterof a square mile in the vicinity of the Indian lake Some ofthe rock has been used in the construction of the dam. There aremany good exposures, the best being at the dam and in the quarriesjust east. Where fresh the rock is greenish gray, and whereweathered it is pinkish. The rock is always coarse grained andrather gneissoid with the porphyritic texture usually well developedthough at times only poorly so. The feldspar phenocrysts are alwayshighly granulated. Locally biotitic shear zones occur. At timessome small Grenville gneiss inclusions may be seen. A thin section of the typical rock from near the dam shows thefollowing mineral percentages: orthoclase 10; microline 25; micro-perthite 15; oligoclase to andesine 4; quartz 40; hornblende 2;biotite I; garnet 2; apatite ^ ; and a little zircon and magnetite. Plate 8. Photo by W. J. Miller, 1914 The State dam at the end of Indian lake. All of the rock is granite porphyry. Avertical fault surface is visible at the end of the footbridge. GEOLOGY OF THE BLUE MOUNTAIN QUADRANGLE 31 Mixed Gneisses General statements. Under this caption are included chieflyGrenville rocks which are cut to pieces by, and more or less closelyinvolved with, various facies of the syenite-granite body. Some-times the Grenville, and sometimes the igneous, rocks prevail. Ofthe igneous rocks in most of the areas, granite appears to pre-dominate. In general it may be said that these mixed gneissesinclude: long, narrow masses of Grenville and syenite or granitedistinctly recognizable as such but showing rapid alterations atright angles to the strike of the foliation; bodies of syenite or granitecontaining numerous sharply defined lenslike inclusions of Gren-ville ; Grenville rocks intimately shot through by igneous rocks afterthe fashion of so-call
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Keywords: ., bookauthorne, bookcentury1900, bookdecade1910, booksubjectscience
