Annual report . dering the prominence of foliation in the gneissicseries. The effects of dynamic metamorphism are chiefly in theform of strain shadows in the quartzes. Glenham gneiss. The prevailing and characteristic surface rockof the Glenham belt is a granitic gneiss. It appears to be an alteredderivative of other gneisses which are entirely similar to those ofthe Highlands, and which are exposed in places within the belt. The surface gneiss isfoliated in certain por-tions, while in others itis massive. There areminor variations in tex-ture and in mineralogywhich depend upon bothan ancient
Annual report . dering the prominence of foliation in the gneissicseries. The effects of dynamic metamorphism are chiefly in theform of strain shadows in the quartzes. Glenham gneiss. The prevailing and characteristic surface rockof the Glenham belt is a granitic gneiss. It appears to be an alteredderivative of other gneisses which are entirely similar to those ofthe Highlands, and which are exposed in places within the belt. The surface gneiss isfoliated in certain por-tions, while in others itis massive. There areminor variations in tex-ture and in mineralogywhich depend upon bothan ancient and a morerecent alteration. Thesevarieties grade into oneanother. The gneiss isusually red from dis-seminated iron stainsand over much of thebelt is deeply chlorit-ized. The thin sectionshows abundant quartzwith orthoclase, microcline, plagioclase, and biotite altered to chlor-ite. Magnetite is abundant and zircons are occasional. Occasionally the rock consists of feldspar and quartz with verylittle or no Fig. 7 Glenham gneiss. Actual size 3 mm. Q, quartz;M, microcline; P, plagioclase; Cb, chlorite after biotite, carrying magnetite OUTCROP OE THE FISHKILL .MOUNTAIN GNEISSES Matteawan. Gneisses which can be readily traced into those ofthe Fishkill mountains outcrop near their base in the eastern part
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectscience, bookyear1902
