File:The American journal of science (1912) (18153692771).jpg

Title: The American journal of science
Identifier: americanjourna4341912newh (find matches)
Year: 1880 (1880s)
Authors:
Subjects: Science
Publisher: New Haven : J. D. & E. S. Dana
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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Ziegler—Siliceous Oolites of Central Pennsylvania. 119 many grains are angular. At times the nucleus is made up of several grains of quartz. The quartz enlargement of the sand- grain nuclei is fibrous chalcedony, and also the fine chert mosaic deposited in concentric rings, as many as twelve being faintly visible. A few of the quartzes show resorption, presumably by solution which subsequently served to enlarge them, partly replacing the original grain with chalcedony. The same pro- cess is indicated by the absence of definite outlines in some sand grains and their tendency to pass by insensible gradations into the fibrous chalcedony. Many of the oolites are entirely chert or chalcedony, and have completely replaced the nucleus; but even in this case, under crossed nicols the outline of the quartz grain which served as a center of deposition is faintly visible. The quartz-grains appear to be igneous in origin and carry fine trails of dust, and very small inclusions of a mineral Fig. 4. Fig. 5.
Text Appearing After Image:
Fig. 4. Filmore type of siliceous oolite. x 72. Fig. 5. Krainrine type, at contact between calcareous and siliceous oolite, x 32. apparently biotite. Fibrous chalcedony also fills most of the interstices between the oolites, and is usually in indistinct bands parallel to their general outline. Some of the quartzes show a tendency toward secondary enlargement. Very little calcite is present, and that seems to be a secondary infiltration subse- quent to the oolite formation. The sand nuclei vary in size from minute fragments up to •62mm in diameter. The longer diameter often exceeds the shorter four or five times. Type Two : the Altro phase.—The siliceous oolite occurring in the vicinity of Altro is the handsomest in Center County. It is practically pure quartzite in composition, as shown by the following analysis by Wieland :* * This Journal (4), iv, p. 262.

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