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Mole Hill (Virginia)
Mole Hill is a rounded hill composed of basalt, a volcanic rock, formed during the Eocene epoch of the Paleogene period. It is the eroded remnant of what was an active volcano approximately 47 million years ago, making it one of the youngest volcanoes on the east coast of North America. It is located west of Harrisonburg, Virginia, in Rockingham County. Description Mole Hill is an isolated, rounded, tree-covered ''monadnock'' in an otherwise relatively flat valley, surrounded by farmland. The peak of Mole Hill is approximately 1,893 feet (577 meters) above sea level. The basalt itself, outcropping at the crest of the hill, is "dark greenish gray to grayish black, medium grained, and moderately porphyritic. It is an olivine-spinel basalt with abundant large pale green pyroxene and minor yellow-brown olivine phenocrysts." The basalt intrudes through the Ordovician Beekmantown Group of carbonate rocks. Age The basalt at Mole Hill (and other igneous dikes in the area) was o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mole Hill VA 1
Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America * Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpidae moles * Marsupial moles, Australian mammals in the family Notoryctidae, similar to but unrelated to Talpidae moles Other common meanings * Mole, colloquial name for a nevus, a growth on human skin ** Melanocytic nevus, another term for mole * Mole (architecture), a pier, jetty, breakwater, or junction between places separated by water * Mole (espionage), a spy who inserts himself into an organisation in order to spy on it. * Mole (sauce), Mexican sauce made from chili peppers, often including fruits, other spices, or chocolate Arts and entertainment * Adrian Mole, the central character in a series of novels by Sue Townsend * Mole, a main character in the children's novel ''The Wind in the Willows'' by Kenneth Grahame * Mole (Zdeně ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spinel
Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals. Properties Spinel crystallizes in the isometric system; common crystal forms are octahedra, usually twinned. It has no true cleavage, but shows an octahedral parting and a conchoidal fracture. Its hardness is 8, its specific gravity is 3.5–4.1, and it is transparent to opaque with a vitreous to dull luster. It may be colorless, but is usually various shades of red, lavender, blue, green, brown, black, or yellow. Some spinels are among the most famous gemstones; among them are the Black Prince's Ruby and the " Timur ruby" in the British Crown Jewels, and the "Côte de Bretagne", formerly from the French Crown jewels. The Samarian Spinel is the largest known spinel in the world, weighing . The transparent red spinels were called spinel-rubies ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Highland County, Virginia
Highland County is a county located in the Commonwealth of Virginia. As of the 2020 census, the population was 2,232. Its county seat is Monterey. Known as "Virginia's Switzerland" or "Virginia's Little Switzerland", Highland County is the least populous jurisdiction in Virginia, including counties and independent cities. Highland lays claim to being one of the least populous counties and one of the highest average elevations east of the Mississippi River. History Settlement of this portion of the Colony of Virginia by Europeans began around 1745. Located west of the Tidewater and Piedmont regions in Virginia and also west of the Shenandoah Valley, this area is beyond (known in old Virginia as the "Transmountaine") the Blue Ridge Mountains. Rather than cross such a formidable physical barrier, most early settlers came southerly up the Valley across the Potomac River from Maryland and Pennsylvania. Many followed the Great Wagon Road, also known as the Valley Pike (U.S. Route 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trimble Knob
Trimble Knob, located southwest of Monterey, Virginia in Highland County, is a conical hill composed of basalt, a volcanic rock, of Eocene (early Tertiary) age. It is the eroded remnant of what was an active volcano or diatreme that last erupted approximately 35 million years ago, making it one of the youngest volcanos on the east coast of North America. Description Trimble Knob is an isolated conical hill in an otherwise relatively flat valley, surrounded by farmland. The peak of the hill has an elevation of 3123 ft (952m). U.S. Route 220 lies along the southeast flank of the hill. Trimble Knob is the most obvious of many igneous intrusions in the area. The central part of the hill is composed of basalt with a diameter of approximately . The basalt intrudes through the gently dipping Devonian Needmore Formation (fossiliferous shale and calcareous mudstone), and is near the axis of a syncline in the center of the valley. Age The basalt at Trimble Knob (and other igneous di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, where rocks from this period were first studied. The first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. The arthropod groups of myriapods, arachnids and hexapods also became well-established early in this period, after starting their expansion to land at least from the Ordovician period. Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fishes. The placoderms began domina ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiometric Dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. The use of radiometric dating was first published in 1907 by Bertram Boltwood and is now the principal source of information about the absolute age of rocks and other geological features, including the age of fossilized life forms or the age of Earth itself, and can also be used to date a wide range of natural and man-made materials. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geologic time scale. Among the best-known techniques are radiocarbon dating, potassium–argon dating and uranium–lead dating. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Principle Of Cross-cutting Relationships
Cross-cutting relationships is a principle of geology that states that the geologic feature which cuts another is the younger of the two features. It is a relative dating technique in geology. It was first developed by Danish geological pioneer Nicholas Steno in ''Dissertationis prodromus'' (1669) and later formulated by James Hutton in '' Theory of the Earth'' (1795) and embellished upon by Charles Lyell in ''Principles of Geology'' (1830). Types There are several basic types of cross-cutting relationships: *Structural relationships may be faults or fractures cutting through an older rock. *Intrusional relationships occur when an igneous pluton or dike is intruded into pre-existing rocks. *Stratigraphic relationships may be an erosional surface (or unconformity) cuts across older rock layers, geological structures, or other geological features. *Sedimentological relationships occur where currents have eroded or scoured older sediment in a local area to produce, for exam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleozoic
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ''zōḗ'' (), "life", meaning "ancient life" ). It is the longest of the Phanerozoic eras, lasting from , and is subdivided into six geologic periods (from oldest to youngest): # Cambrian # Ordovician # Silurian # Devonian # Carboniferous # Permian The Paleozoic comes after the Neoproterozoic Era of the Proterozoic Eon and is followed by the Mesozoic Era. The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earth's history, known as the Cambrian explosion, in which most modern phyla first appeared. Arthropods, molluscs, fish, amphibians, reptiles, and synapsids all evolved during the Paleozoic. Life began in the ocean bu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dike (geology)
A dike or dyke, in geological usage, is a sheet of rock that is formed in a fracture of a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack then solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack.Essentials of Geology, 3rd Ed, Stephen Marshak Magmatic dikes A magmatic dike is a sheet of igneous rock that cuts across older rock beds. It is formed when magma fills a fracture in the older beds and then cools and solidifies. The dike rock is usually more resistant to weathering than the surrounding rock, so that erosion exposes the dike as a natural wall or ridge. It is from these natural walls that dikes get their name. Dikes preserve a record of the fissures through which most mafic magma (fluid magma low in silica) reaches the surface. They are studied by geologists for the cl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beekmantown Group
The Beekmantown Group is a late Cambrian to lower–middle Ordovician geologic group that occurs in the eastern Canada (Québec) and northeastern United States, datable from its conodont fauna. It contains dolomitic sandstones and carbonates from just off land from the palaeocoastline. The usage of the term is diverse and depends on the state or region in question, and the group encompasses different formations in different regions. In some states it is considered a formation rather than a group, but the lithology varies by region. Geologic Unit, Geolex — Unit Summary, National Geologic Map Database. USGS/AASG. Retrieved 2018-06-11. See also * |
