Natural Bridge - Physical Geology


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Presentation on the formation of the Natural Bridge in Virginia, by Amanda Schwartz.

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Natural Bridge - Physical Geology

  1. 1. Natural Bridge, Virginia<br />Drawing and Etching by Rob Hershelwood<br />By Amanda Schwartz<br />
  2. 2. LOCATION<br />is located in the southern portion of Rockbridge County, Virginia, 14 miles southwest of Lexington and 39 miles northeast of Roanoke. It is situated in the Shenandoah Valley of Virginia .<br />Natural Bridge<br />
  3. 3. The floor of the Shenandoah Valley forms an undulating,but fairly level, lowlandthat contrasts strongly with the ridges that bound it on two sides. <br />Shenandoah National Park<br />
  4. 4. A widespread erosion surface, known as the Valley- floor (or Harrisburg) <br />is well developed in the Natural Bridge region, where its remnantsstand between 1,200 and 1,400 ‘ feet above tide. <br />peneplain<br />Potomac River and level topped ridges near Magnolia, from Sideling Hill; the ridges preserve remnants of the Harrisburg peneplain. Town Hill in the distance. Morgan County, West Virginia. 1911. Plate 4 in U.S. Geological Survey. Folio 179. 1912.<br />
  5. 5. Some of the <br />on this peneplain have developed deep valleys, among them,which flows beneath the bridge. <br />streams<br />Cedar Creek<br />
  6. 6. Part of this process of erosion, the bridge is a massive span of<br />approximately 90feet long and 1oo feet in average width.<br />limestone<br />
  7. 7. How It Formed…<br />A large fissure in the earth, served as a conduit for Cedar Creek to become a subterraneous stream, or “sinking creek” beneath the arch of the present bridge, then only the continuation of the transverse ridge of hills. The stream has gradually widened, and deepened this ravine to its present situation. Fragments of its sides also yielding to the expansion and contraction of heat and cold, have also tumbled down .<br />Frederic Edwin Church. Oil on canvas. 1852<br />
  8. 8. Therocksof the bridge itself, which are limestonesanddolomitesof the Chepultepec formation of late Cambrian age, are substantially horizontal. Their stratification is readily visible both in the walls of the gorge and in the bridge, where there are many vertical joint planes. A broad, open, synclinal structure, called the "Natural Bridge syncline," is present in this part of the Valley of Virginia.<br />
  9. 9. Thomas Jefferson<br />Thomas Jefferson extolled the Natural Bridge in his Notes on the State of Virginia, 1782, consequently drawing national and international attention from travelers, artists, philosophers and writers alike, and turning this rock formation into an early American icon.<br />From Notes on the State of Virginia, by Thomas Jefferson, 1782.<br />
  10. 10. Gilmer, Francis William . “On the Geological Formation of the Natural Bridge of Virginia.” Transactions of the American Philosophical Society, New Series. 1 (American Philosophical Society, 1818), 187-192.<br />Woodward, Herbert P. “Natural Bridge and Natural Tunnel.” The Journal of Geology 44:5 (Chicago: University of Chicago Press, 1936), 604-616.<br />References<br />