![]() The oolites are composed principally of a mineral occurring as minute flakes disposed tangentially to the spherical structure. Broken oolites serving as nuclei for further oolitic growth show that the oolites formed before final deposition of the sediment. They are recognized as oolites by their nuclei and concentric structure and by their spherical form where protected from flattening after deposition. The oolites and other larger grains, which make up less than one-third of the rock, tend to be concentrated in lenses. In thin section chamosite oolites and other sand-sized grains are seen to be scattered through a fine-grained matrix (fig. However, the oolites included in collophane nodules and those protected by shell fragments are only slightly flattened. Their thickness is a small fraction of their width. A few display distinct concentric markings many possess a raised central area which can be identified with the hand lens as a rounded quartz nucleus. Generally, they are oriented parallel to bedding. The oolites are black, shiny, disc-shaped, and range from 1 to 2 mm in diameter. Oxidized oolitic chamosite also occurs at the top of the Montebello Sandstone in Dauphine County, 3 miles north of Amity Hall on U. Although Lesley mentioned neither chamosite oolites nor specific iron minerals, it seems likely that he was dealing with the oxidized chamositic unit. Lesley (1892) described a thin bed of "fossil ore" from the northern slope of Little Mountain and various other localities in Perry County, Pennsylvania. The shale is badly weathered and coated with brown iron oxide. Route 11 where it has the same stratigraphic position as in the Rockville quarry. The oolite-bearing shale is also exposed at the north end of the roadcut in Little Mountain along U. Subspherical collophane nodules up to 25 mm in diameter are randomly distributed throughout the oolitic unit. Both oolites and quartz grains decrease in abundance toward the top of the unit. Scattered small rounded pebbles and sand grains of quartz occur in the basal part of the black shale and in the oolitic lenses. Oolites are mostly confined to small lenses parallel to bedding. The oolite-bearing black silty shale is 3 ft thick and contains abundant marine fossils. Marine fossils occur in the sandstone although they are not common. A light gray, thick-bedded, coarse-grained, fairly wellsorted quartzose sandstone occurs beneath the oolitic unit. The oolites occur in a black, fossiliferous shale at the base of 55 ft of dark gray, thin-bedded, fossiliferous silty and sandy shale (Willard's unit 4). Willard (1939) described the stratigraphy and paleontology of the Rockville quarries. These "spores," restudied by the authors, proved to be flattened chamosite oolites. sp.) in a black shaly siltstone in the Devonian Montebello Sandstone at the northernmost Rockville quarry, 2 miles north of Harrisburg, Pennsylvania. The environment in which the oolites formed was marine, slightly reducing, having a small clastic influx, and with currents strong enough to agitate sand grains.Ĭramer (1958) described spore -like fossils ( Tasmanites rockvillensis n. Previously described " spore -like fossils" in a black silty shale in the Devonian Montebello Sandstone, north of Harrisburg, Pennsylvania, were restudied and found to be flattened chamosite oolites. (December), Pages 585-588 Chamosite Oolites in the Devonian of Pennsylvania
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