Annual report of the United States Geological Survey to the Secretary of the Interior . ns show many inclusions and a wavy extinction; the cement isundergoing partial alteration to limonite. The rock is a calcareousquartz and feldspar grit—a calcareous and feldspathic quartzite. Other finer-grained pebbles consist mainly of rhombs and plates ofcalcite, with fine, angular quartz grains and muscovite scales—aquartzose, micaceous crystalline limestone. A very fine-grained and noncaleareous pebble consists of partly ori-entated muscovite and chlorite scales and quartz grains, with thickly dis-semi
Annual report of the United States Geological Survey to the Secretary of the Interior . ns show many inclusions and a wavy extinction; the cement isundergoing partial alteration to limonite. The rock is a calcareousquartz and feldspar grit—a calcareous and feldspathic quartzite. Other finer-grained pebbles consist mainly of rhombs and plates ofcalcite, with fine, angular quartz grains and muscovite scales—aquartzose, micaceous crystalline limestone. A very fine-grained and noncaleareous pebble consists of partly ori-entated muscovite and chlorite scales and quartz grains, with thickly dis-seminated spherules or crystals of pyrite, partly altered to limonite—afine, micaceous quartzite, or a quartzose mica-schist. SOURCES OF THE PEBBLES. The pre-Cambrian must naturally be regarded as the source of thegranitic or gneissic quartz pebbles (frequently bluish or pinkish), amialso of the feldspar grains, but either the Cambrian or the OrdovicianSupplied the crystalline Limestone and the calcareous and micaceous U. S. GEOLOGICAL SURVEY TWENTIETH ANNUAL REPORT PART II PL. II. IS BIRD MOUNTAIN GENERAL VIEW, FROM A POINT I] MILES SOUTH-SOUTHWEST OF SUMM IT. UbKAM OF THE UNIVERSITY df ILLINOIS. DALE.] THE SCHIST. 19 quartzite, as well as the carbonate of iron. The writer is notacquainted with an}- similar deposit of carbonate in the Taconicregion. THE SCHIST. A purplish schist from the north foot of the mountain shows the finelyplicated sericite, quartz, hematite dots, and many actinolite prismslying in all directions. A green schist from the ravine on the north-northwest side (1,100-foot contour) is like the purple, but has chloriteand no hematite, and the plications have resulted in the usual slipcleavage. A similar schist occurs also at the foot of the talus on thewestern side of the summit. In all these specimens the actinolite prismsproduce a fine speckling. Such schists recur also on the eastern sideof the mountain, but the actinolite is not always present. In the sc
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