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83-676: Wissahickon Creek is a tributary of the Schuylkill River in Montgomery and Philadelphia Counties, Pennsylvania . Wissahickon Creek rises in Montgomery County, runs approximately 23 miles (37 km) passing through and dividing Northwest Philadelphia before emptying into the Schuylkill River at Philadelphia . Its watershed covers about 64 square miles (170 km). Much of the creek now runs through or next to parkland, with

166-559: A pegmatitic gabbro ) is a coarse-grained rock containing patches of much coarser-grained rock of essentially the same composition. Individual crystals in pegmatites can be enormous in size. It is likely that the largest crystals ever found were feldspar crystals in pegmatites from Karelia with masses of thousands of tons. Quartz crystals with masses measured in thousands of pounds and micas over 10 meters (33 ft) across and 4 meters (13 ft) thick have been found. Spodumene crystals over 12 meters (40 ft) long have been found in

249-648: A talc schist which contains the mineral talc, so soft it can be scratched with a fingernail. In 1694, Johannes Kelpius arrived in Philadelphia with a group of like-minded German Pietists to live in the valley of the Wissahickon Creek. They formed a monastic community and became known as the Hermits or Mystics of the Wissahickon. Kelpius was a musician, writer, and occultist . He frequently meditated (some believe in

332-461: A cave—the Cave of Kelpius 40°01′25″N 75°12′02″W  /  40.023544°N 75.200665°W  / 40.023544; -75.200665 ) along the banks of the Wissahickon and awaited the end of the world, which was expected in 1694. No sign or revelation accompanied that year, but the faithful continued to live in celibacy by the stream, searching the stars and hoping for the end. Kelpius described

415-440: A common building material in the 19th and early 20th centuries. In addition to Wissahickon schist, there are layers of quartzite in the valley. Both schist and quartzite are metamorphic rocks formed from sedimentary deposits of mud and sand that one time were washed from ancient continents into a shallow sea. These sedimentary deposits were over time compressed into shale and sandstone. During long periods of mountain building,

498-412: A composition similar to granite , so that their most common minerals are quartz , feldspar , and mica . However, other pegmatite compositions are known, including compositions similar to nepheline syenite or gabbro . The term pegmatite is thus purely a textural description. Geologists typically prefix the term with a compositional description, so that granitic pegmatite is a pegmatite with

581-450: A few pegmatites have a complex composition, with numerous unusual minerals of rare elements. These complex pegmatites are mined for lithium , beryllium , boron , fluorine , tin , tantalum , niobium , rare earth elements , uranium , and other valuable commodities. The word pegmatite derives from Homeric Greek , πήγνυμι ( pēgnymi ), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in

664-574: A fountain sculpture by Alexander Stirling Calder that is located in the center of Logan Circle , also known by its historic name Logan Square , in Philadelphia, contains three large Native American figures that symbolize the area's major streams: the Delaware, the Schuylkill, and the Wissahickon. The young girl leaning on her side against an agitated, water-spouting swan represents the Wissahickon Creek. Tributary A tributary , or an affluent ,

747-611: A higher aluminium content (peraluminous granites). Intermediate pegmatites (NYF + LCT pegmatites) are known and may have formed by contamination of an initially NYF magma body with melted undepleted supracrustral rock. Pegmatites often contain rare elements and gemstones . Examples include aquamarine , tourmaline, topaz, fluorite, apatite, and corundum , often along with tin , rare earth, and tungsten minerals, among others. Pegmatites have been mined for both quartz and feldspar. For quartz mining, pegmatites with central quartz masses have been of particular interest. Pegmatites are

830-522: A literary and artistic movement known as Romanticism. Romantics valued heroism and chivalry in people, and regarded the wild, free, and untamed nature as the "natural" model of true beauty . Philadelphians finally came to value their Wissahickon valley for its wild character. Even when the mills were still operating, there were remote stretches of wild bluffs and overarching trees; now the old mills had become romantic and picturesque, with mossy stone walls suggesting medieval ruins. In 1924, area residents formed

913-562: A lofty tree growing in the sea itself, raised its head above the apparent waters. Except the setting-sun sending his horizontal beams through all the variety of reds and yellows of the branches of the trees in Long Island, and giving, at the same time, a sort of silver cast to the verdure beneath them, I have never seen anything so beautiful as the foggy valley of the Wysihicken. Actress Fanny Kemble , grandmother to novelist Owen Wister , visited

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996-400: A new river, to be given its own name, perhaps one already known to the people who live upon its banks. Conversely, explorers approaching a new land from the sea encounter its rivers at their mouths, where they name them on their charts, then, following a river upstream, encounter each tributary as a forking of the stream to the right and to the left, which then appear on their charts as such; or

1079-500: A policeman patrolled the span, questioning all pedestrians walking the bridge. Once the stream enters the city of Philadelphia, the creek valley and its deeply wooded gorge form part of the Fairmount Park system in Philadelphia, a jewel of a park and of nature set in the middle of an urban landscape. The park here is a ruggedly beautiful valley for the naturalists, artists, fishermen, bicyclists, equestrians, and hikers who are drawn to

1162-485: A private toll road , the Wissahickon Turnpike, linked the entire valley. Long gone were the religious mystics; here instead the mills of Wissahickon Creek made paper, cloth, gunpowder, sawed lumber, milled wheat and corn, and pressed oil from flax. A sizable population worked at the mills and lived in the valley in small villages like Rittenhousetown and Pumpkinville. The nation was becoming an industrial nation, and

1245-449: A rate ranging from 1 m to 10 m per day. Pegmatites are the last part of a magma body to crystallize. This final fluid fraction is enriched in volatile and trace elements. The residual magma undergoes phase separation into a melt phase and a hydrous fluid phase saturated with silica , alkalis , and other elements. Such phase separation requires formation from a wet magma, rich enough in water to saturate before more than two-thirds of

1328-400: A river or stream that branches off from and flows away from the main stream. Distributaries are most often found in river deltas . Right tributary , or right-bank tributary , and left tributary , or left-bank tributary , describe the orientation of the tributary relative to the flow of the main stem river. These terms are defined from the perspective of looking downstream, that is, facing

1411-459: A rock overlooking the valley to drop balls of yarn which contained messages about British troop movements during the occupation of Philadelphia. This is likely a legend, for other stories speak of a witch named Mom Rinkle who had little to do with the Revolution. There is a Mom Rinker's Rock in the park today. Not until 1826 were the cliffs near the creek's mouth blasted away to provide access to

1494-1042: A simple composition, often being composed entirely of minerals common in granite, such as feldspar, mica, and quartz. The feldspar and quartz often show graphic texture . Rarely, pegmatites are extremely enriched in incompatible elements , such as lithium , caesium , beryllium , tin , niobium , zirconium , uranium , thorium , boron, phosphorus, and fluorine. These complex pegmatites contain unusual minerals of these elements, such as beryl, spodumene, lepidolite, amblygonite, topaz, apatite, fluorite, tourmaline, triphylite , columbite , monazite , and molybdenite . Some of these can be important ore minerals. Some gemstones , such as emerald , are found almost exclusively in pegmatites. Nepheline syenite pegmatites typically contain zirconium, titanium , and rare earth element minerals. Gabbroic pegmatites typically consist of exceptionally coarse interlocking pyroxene and plagioclase . Pegmatites are enriched in volatile and incompatible elements , consistent with their likely origin as

1577-518: Is Wise's (2022) pegmatite classification, which focuses mostly on the source of the magma from which the pegmatite crystalizes. Pegmatites form under conditions in which the rate of new crystal nucleation is much slower than the rate of crystal growth . Large crystals are favored. In normal igneous rocks, coarse texture is a result of slow cooling deep underground. It is not clear if pegmatite forms by slow or rapid cooling. In some studies, crystals in pegmatitic conditions have been recorded to grow at

1660-446: Is a stream or river that flows into a larger stream ( main stem or "parent" ), river, or a lake . A tributary does not flow directly into a sea or ocean . Tributaries, and the main stem river into which they flow, drain the surrounding drainage basin of its surface water and groundwater , leading the water out into an ocean. The Irtysh is a chief tributary of the Ob river and

1743-850: Is a chilled margin whose composition is representative of the original melt. Pegmatites derived from batholiths can be divided into a family of NYF pegmatites, characterized by progressive enrichment in niobium , yttrium , and fluorine as well as enrichment in beryllium, rare earth elements, scandium , titanium, zirconium, thorium, and uranium; and a family of LCT pegmatites, characterized by progressive accumulation of lithium, caesium , and tantalum, as well as enrichment in rubidium , beryllium, tin, barium, phosphorus, and fluorine. The NYF pegmatites likely fractionated from A- to I-type granites that were relatively low in aluminium (subaluminous to metaluminous granites). These granites originated from depleted crust or mantle rock. LCT pegmatites most likely formed from S-type granites or possibly I-type granites, with

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1826-675: Is a swimming area on the mouth of Cresheim Creek . As the ravine widens into the Cresheim, the waters gather in a basin surrounded on either side by rocky outcroppings before flowing into the Wissahickon Creek. Legend has it that the Native American Lenape tribes used this as a spiritual area, where local author Phyllis Knapp Thomas writes that "...the Good Spirit is claimed to have banished the Evil Spirit into deep, dark waters". Although it

1909-411: Is also the longest tributary river in the world with a length of 4,248 km (2,640 mi). The Madeira River is the largest tributary river by volume in the world with an average discharge of 31,200 m /s (1.1 million cu ft/s). A confluence , where two or more bodies of water meet, usually refers to the joining of tributaries. The opposite to a tributary is a distributary ,

1992-427: Is broad agreement on the basic mechanisms by which they form, the details of pegmatite formation remain enigmatic. Pegmatites have characteristics inconsistent with other igneous intrusions. They are not porphyritic , and show no chilled margin . On the contrary, the largest crystals are often found on the margins of the pegmatite body. While aplites are sometimes found on the margins, they are as likely to occur within

2075-467: Is followed by deposition of albite , lepidolite , gem tourmaline , beryl, spodumene, amblygonite , topaz , apatite , and fluorite , which may partially replace some of the minerals in the earlier zone. The center of the pegmatite may have cavities lined with spectacular gemstone crystals. Some pegmatites have more complex zoning. Five distinct zones are recognized in the Harding Pegmatite in

2158-489: Is found. Pegmatites are found as irregular dikes , sills , or veins , and are most common at the margins of batholiths (great masses of intrusive igneous rock). Most are closely related spatially and genetically to large intrusions. They may take the form of veins or dikes in the intrusion itself, but more commonly, they extend into the surrounding country rock, especially above the intrusion. Some pegmatites surrounded by metamorphic rock have no obvious connection to

2241-504: Is not legal due to unsafe levels of pollutants, Devil's pool has become a popular area to swim, lounge, and drink. Unfortunately, Devil's pool often falls victim to litter and vandalism. However, recent efforts to clean the site by the Friends of the Wissahickon have been moderately successful. Another outlook in the park is Mom Rinker's Rock , on a ridge on the eastern side of the Park just north of

2324-460: Is on the order of magnitude of one to a few hundred meters. Compared to typical igneous rocks they are rather inhomogeneous and may show zones with different mineral assemblages. Crystal size and mineral assemblages are usually oriented parallel to the wall rock or even concentric for pegmatite lenses. Modern pegmatite classification schemes are strongly influenced by the depth-zone classification of granitic rocks published by Buddington (1959), and

2407-520: Is one of fewer than 600 National Natural Landmarks in America. Recently, interest in reintroducing brook trout to the Wissahickon Valley portion of Fairmount park has been growing. Among the earliest references to the valley was by William Cobbett in his book Rural Rides , which takes the form of a series of letters. In one dated 1821 he said, These are the fogs that sweep off the new settlers in

2490-512: The Black Hills of South Dakota , and beryl crystals 8.2 meters (27 ft) long and 1.8 meters (6 ft) in diameter have been found at Albany, Maine . The largest beryl crystal ever found was from Malakialina on Madagascar, weighing about 380 tons, with a length of 18 m (59 ft) and a crosscut of 3.5 m (11 ft). Pegmatite bodies are usually of minor size compared to typical intrusive rock bodies. Pegmatite body size

2573-503: The Picuris Mountains of northern New Mexico , US. These are: Large crystals nucleate on the margins of pegmatites, becoming larger as they grow inward. These include very large conical alkali feldspar crystals. Aplites are commonly present. These may cut across the pegmatite, but also form zones or irregular patches around coarser material. The aplites are often layered, showing evidence of deformation. Xenoliths may be found in

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2656-492: The Revolutionary War Battle of Germantown , which was fought not too far from the stream. The American General John Armstrong , compelled by the rough terrain to abandon a cannon in the valley, expressed his contempt for the "horrendous hills of the Wissahickon." Later legends tell of American spies taking advantage of the terrain to retrieve information from an informant named Mom Rinker , who allegedly perched atop

2739-459: The texture known as graphic granite . The term was first used by René Just Haüy in 1822 as a synonym for graphic granite . Wilhelm Karl Ritter von Haidinger first used the term in its present meaning in 1845. Pegmatites are exceptionally coarse-grained igneous rocks composed of interlocking crystals , with individual crystals usually over 1 centimeter (0.4 in) in size and sometimes exceeding 1 meter (3 ft). Most pegmatites have

2822-609: The American woods. I remember a valley in Pennsylvania, in a part called Wysihicken [ sic ]. In looking from a hill, over this valley, early in the morning, in November, it presented one of the most beautiful sights that my eyes ever beheld. It was a sea bordered with beautifully formed trees of endless variety of colours. As the hills formed the outsides of the sea, some of the trees showed only their tops; and, every now and then,

2905-735: The Chiliast dreams of Petersen. Deep in the woods, where the small river slid Snake-like in shape, the Helmstadt mystic hid, Weird as a wizard over arts forbid. Christopher Morley also portrayed the valley's beauty in his writings. The Wissahickon is mentioned very briefly in A Biography of the Poet, Sidney Lanier by Edwin Mims. Mark Twain mentioned the Wissahickon during the short time he spent in Philadelphia working for The Philadelphia Inquirer : "Unlike New York, I like this Philadelphia amazingly, and

2988-555: The Dunkards and the Ephrata Cloister built a stone house on land previously owned by Dunkards. The structure, used for church retreats, still stands today, and is known as The Monastery , a remaining witness to the Wissahickon's days as an isolated religious refuge. The same steep slopes and gorge that provided an attractive isolation to religious adherents in the 17th and early 18th centuries provided an efficient source of energy for

3071-487: The East Falls-Germantown neighborhoods in Philadelphia. It was completed in 1932 and is 915 feet (279 m) long, 84 feet (26 m) wide, and 185 feet (56 m) above water. It was originally designed to carry a planned extension of a subway into Roxborough, but the subway never reached the bridge. The bridge has been known as a suicide bridge since its opening. Beginning in 1941 for an unknown duration of time

3154-498: The Fly (Frank Amato Publications, 2005) and Small Fry: The Lure of the Little (The Whitefish Press, 2009). Both books describe the Wissahickon Valley and the experience of fly fishing along Wissahickon Creek in the early twenty-first century. Artists have portrayed the stream and its valley: There exists a Currier and Ives Scenery Of The Wissahickon The Swann Memorial Fountain (1924),

3237-490: The Ginsburg & Rodionov (1960) and Ginsburg et al. (1979) classification which categorized pegmatites according to their depth of emplacement and relationship to metamorphism and granitic plutons. Cerny’s (1991) revision of that classification scheme is widely used, Cerny’s (1991) pegmatite classification, which is a combination of emplacement depth, metamorphic grade and minor element content, has provided significant insight into

3320-676: The Kibara Belt of Rwanda and Democratic Republic of the Congo , the Kenticha mine of Ethiopia the Alto Ligonha Province of Mozambique , and the Mibra (Volta) mine of Minas Gerais , Brazil. Notable pegmatite occurrences are found worldwide within the major cratons , and within greenschist -facies metamorphic belts. However, pegmatite localities are only well recorded when economic mineralisation

3403-658: The Secret History of the Declaration of Independence (1847) may refer not only to the Wissahickon, but to his wife, the former Rose Newman. He wrote: A poem of everlasting beauty and a dream of magnificance – the world-hidden, wood embowered Wissahickon. Depending on one of Lippard's mostly contrived stories, John Greenleaf Whittier wrote about Johannes Kelpius and his followers on the Wissahickon in his 1872 poem Pennsylvania Pilgrim : Or painful Kelpius from his hermit den By Wissahickon, maddest of good men, Dreamed o'er

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3486-726: The Walnut Lane Bridge. A tremendous variety of geology is evident along Wissahickon Creek. Three of the geologic regions that the stream passes through are the Newark Basin of Triassic sandstone and shale , the limestone and dolomite of the Chester Valley, and the Wissahickon Formation where the waters of the stream flow into the Schuylkill and eventually the Delaware Rivers. A unique and very distinctive rock of

3569-507: The Wissahiccon ", in which he wrote: Now the Wissahiccon is of so remarkable a loveliness that, were it flowing in England, it would be the theme of every bard, and the common topic of every tongue, if, indeed, its banks were not parcelled off in lots, at an exorbitant price, as building-sites for the villas of the opulent. Yet it is only within a very few years that any one has more than heard of

3652-431: The Wissahiccon ... the brook is narrow. Its banks are generally, indeed almost universally, precipitous, and consist of high hills, clothed with noble shrubbery near the water, and crowned at a greater elevation, with some of the most magnificent forest trees of America, among which stands conspicuous the liriodendron tulipiferum . The immediate shores, however, are of granite, sharply defined or moss-covered, against which

3735-431: The Wissahickon Creek valley is Wissahickon schist , the predominant bedrock underlying the Philadelphia region, found over a broad swath of southeastern Pennsylvania from Trenton into Delaware and Maryland. This Precambrian to Cambrian stone, first studied in the Wissahickon gorge, has flecks of glittery mica , small garnets , and many-toned shadings of gray, brown, tan, and blue, and is attractive enough to have become

3818-479: The Wissahickon was leading the way. Benjamin Franklin already had noted in his will the high elevation and quality of Wissahickon water, proposing that in some future day the stream be dammed to supply a safe and pure water source for Philadelphia's water supply, and even allocating funds for this purpose. This did not happen, but the quest for pure water affected the Wissahickon's subsequent history. Seeking to prevent

3901-455: The body of the pegmatite, but their original mineral content is replaced by quartz and alkali feldspar, so that they are difficult to distinguish from the surrounding pegmatite. Pegmatite also commonly replaces part of the surrounding country rock. Because pegmatites likely crystallize from a fluid-dominated phase, rather than a melt phase, they straddle the boundary between hydrothermal mineral deposits and igneous intrusions . Although there

3984-488: The body of the pegmatite. The crystals are never aligned in a way that would indicate flow, but are perpendicular to the walls. This implies formation in a static environment. Some pegmatities take the form of isolated pods, with no obvious feeder conduit. As a result, metamorphic or metasomatic origins have sometimes been suggested for pegmatites. A metamorphic pegmatite would be formed by removal of volatiles from metamorphic rocks, particularly felsic gneiss , to liberate

4067-426: The classification is the petrogenetic component of the classification, which shows the association of LCT pegmatites with mainly orogenic plutons, and NYF pegmatites with mainly anorogenic plutons. Lately, there have been a few attempts to create a new classification for pegmatites less dependent on mineralogy and more reflective of their geological setting. On this issue, one of the most notable efforts on this matter

4150-412: The cluster of mills at Rittenhousetown , approximately 1.5 mi (2.4 km) up the creek on Paper Mill Run (also known as Monoshone Creek), a small tributary of the Wissahickon. Here William Rittenhouse (grandfather of the astronomer David Rittenhouse ) had in the early 18th century built the first paper mill in America. Gradually this road and other mill access roads were connected, and in 1856

4233-425: The coal fields far upstream beyond Philadelphia's control, but the waters of the Wissahickon had been restored and the beauty of the Wissahickon Valley had been preserved. Most of America became more industrialized, but the Wissahickon valley quietly returned to its original wilderness character. The reason the Wissahickon Valley retained its wilderness character, even after its clean waters were no longer essential to

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4316-481: The composition of granite while nepheline syenite pegmatite is a pegmatite with the composition of nepheline syenite. However, the British Geological Survey (BGS) discourages this usage, preferring terms like biotite-quartz-feldspar pegmatite for a pegmatite with a typical granitic composition, dominated by feldspar with lesser quartz and biotite. Under BGS terminology, a pegmatitic rock (for example,

4399-432: The development of water mills in later years. One miller had by 1690 already constructed a dam, sawmill, gristmill, and house by the narrow shelf of land at the confluence of the Wissahickon with the Schuylkill River, but the rugged terrain of the valley forestalled further development alongside the stream itself. By 1730, however, eight mills had been constructed, and by 1793, twenty-four, along with many dams. Most of America

4482-421: The direction the water current of the main stem is going. In a navigational context, if one were floating on a raft or other vessel in the main stream, this would be the side the tributary enters from as one floats past; alternately, if one were floating down the tributary, the main stream meets it on the opposite bank of the tributary. This information may be used to avoid turbulent water by moving towards

4565-511: The earliest map of this region of Pennsylvania, by Thomas Holme , the stream is called Whitpaine's creek , after one of the original settlers Richard Whitpaine, who owned several large tracts on the creek. Whitpaine was an early land owner in the days of William Penn . Though at first fairly tame, in its last 7 miles (11 km), the Wissahickon stream drops over 100 feet (30 m) in altitude. Its dramatic geography and dense forest attract thousands of walkers, riders, and bikers. Devil's Pool

4648-402: The final melt fraction of a crystallizing body of magma. However, it is difficult to get a representative composition of a pegmatite, due to the large size of the constituent mineral crystals. Hence, pegmatite is often characterised by sampling the individual minerals that compose the pegmatite, and comparisons are made according to mineral chemistry. A common error is to assume that the wall zone

4731-631: The first-order tributary being typically the least in size. For example, a second-order tributary would be the result of two or more first-order tributaries combining to form the second-order tributary. Another method is to list tributaries from mouth to source, in the form of a tree structure , stored as a tree data structure . Pegmatite Many of the world's largest crystals are found within pegmatites. These include crystals of microcline , quartz , mica , spodumene , beryl , and tourmaline . Some individual crystals are over 10 m (33 ft) long. Most pegmatites are thought to form from

4814-451: The handedness is from the point of view of an observer facing upstream. For instance, Steer Creek has a left tributary which is called Right Fork Steer Creek. These naming conventions are reflective of the circumstances of a particular river's identification and charting: people living along the banks of a river, with a name known to them, may then float down the river in exploration, and each tributary joining it as they pass by appears as

4897-556: The hydrous phase is completely depolymerized, existing almost entirely as orthosilicate , with all oxygen bridges between silicon ions broken. The low viscosity promotes rapid diffusion through the fluid, allowing growth of large crystals. When this hydrous fluid is injected into the surrounding country rock , minerals crystallize from the outside in to form a zoned pegmatite, with different minerals predominating in concentric zones. A typical sequence of deposition begins with microcline and quartz, with minor schorl and garnet . This

4980-574: The last few miles running through a deep gorge. The beauty of this area attracted the attention of literary personages like Edgar Allan Poe and John Greenleaf Whittier . The gorge area is now part of Wissahickon Valley Park in Philadelphia, and the Wissahickon Valley is known as one of 600 National Natural Landmarks of the United States. The name of the creek comes from the Lenape word wiessahitkonk, for "catfish creek" or "stream of yellowish color". On

5063-418: The last fluid fraction of a large crystallizing magma body. This residual fluid is highly enriched in volatiles and trace elements, and its very low viscosity allows components to migrate rapidly to join an existing crystal rather than coming together to form new crystals. This allows a few very large crystals to form. While most pegmatites have a simple composition of minerals common in ordinary igneous rock,

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5146-456: The magma is crystallized. Otherwise, the separation of the fluid phase is difficult to explain. Granite requires a water content of 4 wt% at a pressure of 0.5  GPa (72,500  psi ), but only 1.5 wt% at 0.1 GPa (14,500 psi) for phase separation to take place. The volatiles (primarily water, borates , fluorides , chlorides , and phosphates ) are concentrated in the hydrous phase, greatly lowering its viscosity. The silica in

5229-458: The non-profit group "Friends of the Wissahickon", which still works to maintain the park's unique landscape to this day. Remarks on the Wissahickon in literature by such as Fanny Kemble, Edgar Allan Poe, George Lippard, and others are noted below. However much the stream and its valley were appreciated, it still divided parts of the city. To help overcome this, in 1906 the Walnut Lane Bridge

5312-406: The opposite bank before approaching the confluence. An early tributary is a tributary that joins the main stem river closer to its source than its mouth, that is, before the river's midpoint ; a late tributary joins the main stem further downstream, closer to its mouth than to its source, that is, after the midpoint. In the United States, where tributaries sometimes have the same name as

5395-653: The origin of pegmatitic melts and their relative degrees of fractionation. Granitic pegmatites are commonly ranked into three hierarchies (class – family – type – subtype) depending upon their mineralogical-geochemical characteristics and depth of emplacement according to Cerny (1991). Classes are Abyssal, Muscovite, Rare-Element and Miarolitic. The Rare-Element Class is subdivided based on composition into LCT and NYF families: LCT for Lithium, Cesium, and Tantalum enrichment and NYF for Niobium, Yttrium, and Fluorine enrichment. Most authors classify pegmatites according to LCT- and NYF-types and subtypes. Another important contribution of

5478-500: The pellucid water lolls in its gentle flow, as the blue waves of the Mediterranean upon the steps of her palaces of marble. The erratic and almost forgotten novelist George Lippard frequently wrote about the Wissahickon, and was even married at sunset on or around May 14, 1847, on a rocky crag called Mom Rinker's Rock , overlooking the stream. One of his books, The Rose of Wissahikon; or, The Fourth of July, 1776. A Romance, Embracing

5561-448: The people in it ... I saw small steamboats, with their signs up—"For Wissahickon and Manayunk 25 cents". Geo. Lippard, in his Legends of Washington and his Generals, has rendered the Wissahickon sacred in my eyes, and I shall make that trip, as well as one to Germantown, soon ..." Ron P. Swegman , a fly fishing angler, artist, and author, wrote extensively about Wissahickon Creek in two illustrated essay collections, Philadelphia on

5644-431: The picturesque mill, the smooth open field, along whose side the river waters, after receiving this child of the mountains into their bosom, wound deep, and bright, and still, the whole radiant with the softest light I ever beheld, formed a most enchanting and serene subject of contemplation. Edgar Allan Poe alluded to Fanny Kemble's writing in his description of a beautiful Wissahickon valley in his 1844 essay " Morning on

5727-465: The primary source of lithium either as spodumene, lithiophyllite or usually from lepidolite. The primary source for caesium is pollucite , a mineral from a zoned pegmatite. The majority of the world's beryllium is sourced from non-gem quality beryl within pegmatite. Tantalum, niobium, and rare-earth elements are sourced from a few pegmatites worldwide, such as the Greenbushes Pegmatite ,

5810-439: The right constituents and water, at the right temperature. A metasomatic pegmatite would be formed by hydrothermal circulation of hot alteration fluids upon a rock mass, with bulk chemical and textural change. Metasomatism is currently not favored as a mechanism for pegmatite formation and it is likely that metamorphism and magmatism are both contributors toward the conditions necessary for pegmatite genesis. Most pegmatites have

5893-643: The river into which they feed, they are called forks . These are typically designated by compass direction. For example, the American River in California receives flow from its North, Middle, and South forks. The Chicago River 's North Branch has the East, West, and Middle Fork; the South Branch has its South Fork, and used to have a West Fork as well (now filled in). Forks are sometimes designated as right or left. Here,

5976-434: The shale and sandstone were slowly transformed into the schist and quartzite found today. In some places, the compression and heat were extreme enough to fuse the schist with emerging igneous rocks into hard-banded gneiss . Other rocks in the valley are layers of igneous pegmatite and remains of granite plutons , embedded crystals within the schist. A few locations close to Devil's Pool and along Bell's Mill Road have

6059-418: The smaller stream designated the little fork, the larger either retaining its name unmodified, or receives the designation big . Tributaries are sometimes listed starting with those nearest to the source of the river and ending with those nearest to the mouth of the river . The Strahler stream order examines the arrangement of tributaries in a hierarchy of first, second, third and higher orders, with

6142-399: The stream in 1832; her writing awakened a more general interest in the stream and its valley. Her description of the gorge's dramatic end at the stream's confluence with the Schuylkill River and her verse To the Wissahickon both sparked a keen interest in this natural treasure often overlooked by its neighbors. She wrote: The thick, bright, rich-tufted cedars, basking in the warm amber glow,

6225-481: The stream's industrial discharges from affecting the purity of the water of the Schuylkill River, the Fairmount Park Commission took title of much of the land along the Wissahickon in 1869-1870, and continued to expand its holdings in subsequent decades. The mills were razed; the last active mill was demolished in 1884. Several decades later the Schuylkill River itself became seriously polluted by sources in

6308-432: The streams are seen to diverge by the cardinal direction (north, south, east, or west) in which they proceed upstream, sometimes a third stream entering between two others is designated the middle fork; or the streams are distinguished by the relative height of one to the other, as one stream descending over a cataract into another becomes the upper fork, and the one it descends into, the lower ; or by relative volume:

6391-614: The two communities. At least two from the original group, Johann Seelig and Konrad Matthaei, continued as hermits along the Wissahickon into the 1740s. Other religious groups were also associated with the Wissahickon: On Christmas Day in 1723 the first congregation of the Church of the Brethren in America – often called Dunkard Brethren – baptized several new members in the stream. Around 1747, an individual with connections to both

6474-453: The type of meditation he used in his Method of Prayer. (See Further Reading below on this book.) Kelpius died in 1708 and the group disbanded some time thereafter. Some members likely gave up on celibacy and married. A few joined the somewhat like-minded religious colony of Ephrata Cloister under Conrad Beissel in Ephrata , Lancaster County , even though no previous connection existed between

6557-537: The water supply of the city of Philadelphia, was the advent of Romanticism and the changing attitudes which this thought engendered about nature. Before the 19th century, nature had seemed a capricious and ambivalent force, at times a dream, but at times a nightmare. Nature, according to orthodox Christian thought, had fallen with man; though the Renaissance brought about both a new view of mankind and nature, this new attitude took time to grow, but it eventually resulted in

6640-494: The water, and the sidewalks of the bridge 120 feet (37 m) above the Wissahickon. In the past, there was an annual parade of horses, riders, and carriage annually in May for Wissahickon Day, a festive Gala popular among Philadelphia's Equestrians and social elites. The Wissahickon Memorial Bridge , also known as Henry Avenue Bridge, is a stone and concrete bridge that carries Henry Avenue over Wissahickon Creek, joining Roxborough and

6723-428: The wooded, steep banks of the stream. Precipitous wooded inclines that rise more than 200 feet (61 m) above the water create a feeling of remoteness and mountain vastness. There are two main and many smaller bridle paths crossing the park's 1,372 acres (5.55 km) along the Wissahickon Creek. Thomas Mill Covered Bridge , the only covered bridge in a major US city, spans the creek in the park. The Wissahickon Valley

6806-464: Was built over the stream, which was the world's largest concrete arch bridge at the time. The bridge joined the Roxborough and Germantown neighborhoods of Philadelphia, formerly separated by the Wissahickon gorge. The bridge is but 480 feet (150 m) long, with a width of 60 feet (18 m), but its center arch spans an impressive 225 feet (69 m), the crown of the arch is 109 feet (33 m) above

6889-441: Was still wilderness, but the Wissahickon Valley was a developing industrial center. There were more than fifty watermills by 1850, though the thickly forested region about the stream still retained the character of a wilderness. Access roads were being constructed into the steep valley, but there was still no road that followed the stream itself. The nature of the rugged terrain can be comprehended in an event that had occurred during

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