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Harpers Formation
The Harpers Formation is a geologic formation in Maryland, Pennsylvania, Virginia, and West Virginia, consisting of schist, phyllite, and shale. It dates back to the early Cambrian period. It is considered part of the Chilhowee Group. Notable exposures The type section is in gorges of the Potomac River and the Shenandoah River at Harpers Ferry, West Virginia. The Harpers Formation overlies the Ledger Formation (dolomite) due to a thrust fault in small roadside quarry (currently overgrown) on Pottery Hill, southwest of York, Pennsylvania. A. J. Stose and G. W. Stose, 1944. ''Geology of the Hanover-York district'', U. S. Geological Survey Professional paper 204. Gallery File:Quartzite (Harpers Formation, Lower Cambrian; Verona, Virginia, USA).jpg, Quartzite sample of Harpers Formation from near Verona, Virginia File:Jefferson Rock, Harpers Ferry, WV - area view.jpg, Harpers Shale by Jefferson Rock in Harpers Ferry, West Virginia Harpers Phyllite Pottery Hill outcrop 2022.jpg, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metamorphic Rock
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous, sedimentary, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by their protolith, their chemical and mineral makeup, and their texture. They may be formed simply by being deeply buried beneath the Earth's surface, where they are subject to high temperatures and the great pressure of the rock layers above. They can also form from tectonic processes such as continental collisions, which cause horizontal pressure, friction, and distorti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virginia
Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth are shaped by the Blue Ridge Mountains and the Chesapeake Bay, which provide habitat for much of its flora and fauna. The capital of the Commonwealth is Richmond; Virginia Beach is the most-populous city, and Fairfax County is the most-populous political subdivision. The Commonwealth's population was over 8.65million, with 36% of them living in the Baltimore–Washington metropolitan area. The area's history begins with several indigenous groups, including the Powhatan. In 1607, the London Company established the Colony of Virginia as the first permanent English colony in the New World. Virginia's state nickname, the Old Dominion, is a reference to this status. Slave labor and land acquired from displaced native tribes fueled the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Verona, Virginia
Verona is a census-designated place (CDP) in Augusta County, Virginia, United States. The population was 4,239 at the 2010 census. It is part of the Staunton– Waynesboro Micropolitan Statistical Area. History Mount Airy and Verona School are listed on the National Register of Historic Places. Augusta County has announced in 2021 a plan to move the county seat from Staunton to Verona. Geography Verona is located at (38.197048, −79.003116). According to the United States Census Bureau, the CDP has a total area of 7.0 square miles (18.2 km2), of which, 7.0 square miles (18.2 km2) of it is land and 0.14% is water. Demographics As of the census of 2010, there were 4,239 people, 1,457 households, and 984 families residing in the CDP. The population density was 605.6 people per square mile (232.9/km2). There were 1,556 housing units at an average density of 222.3/sq mi (85.5/km2). The racial makeup of the CDP was 88.7% White, 8.3% African ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
York, Pennsylvania
York ( Pennsylvania Dutch: ''Yarrick''), known as the White Rose City (after the symbol of the House of York), is the county seat of York County, Pennsylvania, United States. It is located in the south-central region of the state. The population within York's city limits was 43,718 at the 2010 census, a 7.0% increase from the 2000 census count of 40,862. When combined with the adjacent boroughs of West York and North York and surrounding Spring Garden, West Manchester, and Springettsbury townships, the population of Greater York was 108,386. York is the 11th largest city in Pennsylvania. History 18th century York, also known as Yorktown in the mid 18th to early 19th centuries, was founded in 1741 by settlers from the Philadelphia region and named for the English city of the same name. By 1777, most of the area residents were of either German or Scots-Irish descent. York was incorporated as a borough on September 24, 1787, and as a city on January 11, 1887. York served ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thrust Fault
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If the angle of the fault plane is lower (often less than 15 degrees from the horizontal) and the displacement of the overlying block is large (often in the kilometer range) the fault is called an ''overthrust'' or ''overthrust fault''. Erosion can remove part of the overlying block, creating a ''fenster'' (or ''window'') – when the underlying block is exposed only in a relatively small area. When erosion removes most of the overlying block, leaving island-like remnants resting on the lower block, the remnants are called ''klippen'' (singular ''klippe''). Blind thrust faults If the fault plane terminates before it reaches the Earth's surface, it is referred to as a ''blind thrust'' fault. Because of the lack of surface evidence, blind thr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dolomite (rock)
Dolomite (also known as dolomite rock, dolostone or dolomitic rock) is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite, CaMg(CO3)2. It occurs widely, often in association with limestone and evaporites, though it is less abundant than limestone and rare in Cenozoic rock beds (beds less than about 66 million years in age). The first geologist to distinguish dolomite rock from limestone was Belsazar Hacquet in 1778. Most dolomite was formed as a magnesium replacement of limestone or of lime mud before lithification. The geological process of conversion of calcite to dolomite is known as dolomitization and any intermediate product is known as dolomitic limestone. The "dolomite problem" refers to the vast worldwide depositions of dolomite in the past geologic record in contrast to the limited amounts of dolomite formed in modern times. Recent research has revealed sulfate-reducing bacteria living in anoxic conditions precipitate dolomite which ind ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ledger Formation
The Ledger Formation or Ledger Dolomite is a geologic formation in Pennsylvania, United States. The Ledger is described as light-gray, locally mottled, massive, pure, coarsely crystalline dolomite. It may be siliceous in the middle part. Type section Named from exposures at Ledger, Pennsylvania, formerly 3 miles northeast of Kinzers, Lancaster County, Pennsylvania.Stose, G.W., and Jonas, A.I., 1922. ''The lower Paleozoic section in southeastern Pennsylvania'', Washington Academy of Sciences, Journal v. 12, no. 5, p. 358-36/ref> Other outcrops At Valley Forge National Historical Park, the visitor center parking lot is built within an old quarry of the Ledger, and the former quarry walls are exposed. The rocks contain stromatolites. In the nearby Port Kennedy Quarry, the Triassic Stockton Formation unconformably overlies the folded Ledger. The Harpers Formation overlies the Ledger Formation due to a thrust fault in small roadside quarry (currently overgrown) on Potte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shenandoah River
The Shenandoah River is the principal tributary of the Potomac River, long with two forks approximately long each,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed August 15, 2011 in the U.S. states of Virginia and West Virginia. The river and its tributaries drain the central and lower Shenandoah Valley and the Page Valley in the Appalachians on the west side of the Blue Ridge Mountains, in northwestern Virginia and the Eastern Panhandle of West Virginia. There is a hydroelectric plant along the Shenandoah river constructed in 2014 by Dominion. Course The Shenandoah River is formed northeast of Front Royal near Riverton, by the confluence of the South Fork and the North Fork. It flows northeast across Warren County, passing underneath Interstate 66 from its formation. Beyond the I-66 bridge the river flows through a set of bends before turning to the northeast again, crossing into Clarke County below I-66. Five mi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potomac River
The Potomac River () drains the Mid-Atlantic United States, flowing from the Potomac Highlands into Chesapeake Bay. It is long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map. Retrieved August 15, 2011 with a drainage area of 14,700 square miles (38,000 km2), and is the fourth-largest river along the East Coast of the United States and the 21st-largest in the United States. Over 5 million people live within its watershed. The river forms part of the borders between Maryland and Washington, D.C. on the left descending bank and between West Virginia and Virginia on the right descending bank. Except for a small portion of its headwaters in West Virginia, the North Branch Potomac River is considered part of Maryland to the low-water mark on the opposite bank. The South Branch Potomac River lies completely within the state of West Virginia except for its headwaters, which lie in Virginia. Course The Potomac River runs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Period (geology)
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (scientific branch of geology that aims to determine the age of rocks). It is used primarily by Earth scientists (including geologists, paleontologists, geophysicists, geochemists, and paleoclimatologists) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardized international units of geologic time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phyllite
Phyllite ( ) is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. It is primarily composed of quartz, sericite mica, and chlorite. Phyllite has fine-grained mica flakes, whereas slate has extremely fine mica flakes, and schist has large mica flakes, all mica flakes of which have achieved a preferred orientation. Among foliated metamorphic rocks, it represents a gradation in the degree of metamorphism between slate and schist. The minute crystals of graphite, sericite, or chlorite, or the translucent fine-grained white mica, impart a silky, sometimes golden sheen to the surfaces of cleavage, called "phyllitic luster". The word comes from the Greek ''phyllon'', meaning "leaf". The protolith (or parent rock) for phyllite is shale or pelite, or slate, which in turn came from a shale protolith. Its constituent platy minerals ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schist
Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes or plates. This texture (geology), texture reflects a high content of platy minerals, such as micas, talc, chlorite group, chlorite, or graphite. These are often interleaved with more granular minerals, such as feldspar or quartz. Schist typically forms during regional metamorphism accompanying the process of mountain building (orogeny) and usually reflects a medium Metamorphism#Metamorphic grades, grade of metamorphism. Schist can form from many different kinds of rocks, including sedimentary rocks such as mudstones and igneous rocks such as tuffs. Schist metamorphosed from mudstone is particularly common and is often very rich in mica (a ''mica schist''). Where the type of the original rock (the protolith) is discernible, the schist is us ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
