This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1889 Excerpt: ...into schistose rocks, among which are gneisses. The reasons given for this conclusion are: _ (1) The gradation of the slates into schists, with loss of slaty cleavage, and the development of a foliation, usually oblique to the cleavage, and sometimes even perpendicular to it; (2) the concentric arrangement of the ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1889 Excerpt: ...into schistose rocks, among which are gneisses. The reasons given for this conclusion are: _ (1) The gradation of the slates into schists, with loss of slaty cleavage, and the development of a foliation, usually oblique to the cleavage, and sometimes even perpendicular to it; (2) the concentric arrangement of the schists around granitic areas in such a way that the strike of their foliation is always parallel to the boundaries of the eruptive rock, and the dip always inclined away from them; (3) the clear evidence afforded by the microscope to the effect that the rocks intermediate between the schists and slates have all suffered squeezing to such an extent that their various constituents, more particularly the quartz, have been flattened, cracked, and even broken, so that their different parts extinguish differently; and finally (4) the certainty that much of the material of the schists is of secondary origin. The new minerals produced by the forces at work are silica in different forms, biotite, muscovite, and feldspar, and sometimes hornblende, garnet, tourmaline, and staurolite. In the less schistose varieties the grains of the original slates can be distinguished, as they are outlined by a layer of ferrite deposited upon them before they had lost their characteristic shapes. The quartz grains are flattened in the direction of the line of supposed pressure, and are broken. The cracks are often filled with particles of iron oxides, and sometimes are marked by lines of fluid inclusions. The deposition of silica around the fractured quartz grains and the production of secondary mica and feldspar are regarded as abundantly able to change a slate into a schist, especially when foliation has been 1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Me....
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Add this copy of A Summary of Progress in Mineralogy and Petrography to cart. $47.75, good condition, Sold by Bonita rated 4.0 out of 5 stars, ships from Newport Coast, CA, UNITED STATES, published 2019 by Wentworth Press.