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Septarian concretions (or septarian nodules) are carbonate-rich concretions containing angular cavities or cracks (septaria; sg. septarium, from the Latin septum "partition, separating element", referring to the cracks or cavities separating polygonal blocks of hardened material).
Nodule is also used for widely scattered concretionary lumps of manganese, cobalt, iron, and nickel found on the floors of the world's oceans. This is especially true of manganese nodules. Manganese and phosphorite nodules form on the seafloor and are syndepositional in origin. Thus, technically speaking, they are concretions instead of nodules ...
Top of Stonyman Summit, Shenandoah National Park The geology of Virginia began to form at least 1.8 billion years ago. The oldest rocks in the state were metamorphosed during the Grenville orogeny, a mountain-building event beginning 1.2 billion years ago in the Proterozoic, which obscured older rocks.
Virginia counties and cities by year of establishment. The Commonwealth of Virginia is divided into 95 counties, along with 38 independent cities that are considered county-equivalents for census purposes, totaling 133 second-level subdivisions. In Virginia, cities are co-equal levels of government to counties, but towns are part of counties.
The Chesapeake Bay impact crater is a buried impact crater, located beneath the mouth of Chesapeake Bay, United States. It was formed by a bolide that struck the eastern shore of North America about 35.5 ± 0.3 million years ago, in the late Eocene epoch. It is one of the best-preserved "wet-target" impact craters in the world. [3]
The geologic column in Virginia begins at the Cambrian and spans to the Quaternary. [2] Although present, the state's Cambrian rocks preserve very few fossils and no documented individual deposit has proven a fertile collecting ground. [3] The state was covered by a warm shallow sea at the time. [1]
Outside a specific state plane zone accuracy rapidly declines, thus the system is not useful for regional or national mapping. Most state plane zones are based on either a transverse Mercator projection or a Lambert conformal conic projection. The choice between the two map projections is based on the shape of the state and its zones. States ...
Debates on whether specific forms are pseudo or true fossils can be lengthy and difficult. For example, Eozoön is a complex laminated form of interlayered calcite and serpentine originally found in Precambrian metamorphosed limestones (marbles). It was at first thought to be the remains of a giant fossil protozoan (Dawson, 1865), then by far ...