The Geognosy of the Appalachians and the Origin of Crystalline Rocks: Address to the American Association for the Advancement of Science, on Retiring ... August 16, 1871 (Classic Reprint) - Hardcover

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Excerpt from The Geognosy of the Appalachians and the Origin of Crystalline Rocks: Address to the American Association for the Advancement of Science, on Retiring From the Office of President of the Association, Indianapolis, August 16, 1871

Laurentian gneiss. The coarse-grained, porphyritic, reddish vari eties common to the latter are wanting in the Green Mountains, where the gneiss is generally of pale greenish and grayish hues. Massive stratified diorites, and epidotic and chloritic rocks, often more or less schistose, with steatite, dark colored serpentines and ferriferous dolomites and magnesites also characterize this gneissic series, and are intimately associated with beds of iron ore, generally a Slaty hematite, but occasionally magnetite. Chrome, titanium, nickel, copper, antimony and gold are frequently met with in this se ries. The gneisses often pass into schistose micaceous quartzites, and the argillites, which abound, frequently assume a soft, unctuous character, which has acquired for them the name of talcose or na creous slates, though analysis shows them not to be magnesian, but to consist essentially of a hydrous micaceous mineral. They are sometimes black and graphitic.

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