Bulletin of the Geological Society of America (Volume 3) (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1895 edition. Excerpt: ...visited the above localities, states that these schists are common associates of the crystalline limestones in Canada. The Gneiss.--Assuming that the Cheever mine is in the limestone series, as it appears to be, interesting data are available near the workings. The ore, however, and its containing rocks are so similar to those well within the areas of gneiss at Mineville that hesitation was at first felt about this assumption, but the geologic section left no alternative. Its walls afford massive gneisses. Next the ore, the hanging wall contains plagioclase and an emerald-green pyroxene. A few feet further the minerals are plagioclase, quartz, hornblende, and pyroxene, with a notable microperthitic habit in the plagioclase. Fifty yards away the rock contains microperthite, orthoclase, brown biotite, quartz, which is often included in the feldspar, and almost no plagioclase. Similar gneisses occur in other places above the limestone, and mineralogically they do not differ essentially from others below it. From this evidence and that set forth in connection with figure 6 above, the impression has been strengthened that the limestones will prove to be merely a phase of the great gneisaic series A, to which reference has already been made in the introduction. At a number of localities in Ticonderoga township there is a gneissoid rock, intimately associated with the limestones and schists, containing plagioclase aud often scapolite and a curious lavender-colored pyroxene with a pink tinge. Its optical properties are not essentially different from normal pyroxene, but the color is peculiar. This gneiss is abundant just north of Rogers rock, where it is intimately associated with limestone. The same pyroxene is found in silicate bunches in the...