The Potomac Formation in Virginia

The Potomac Formation in Virginia

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 edition. Excerpt: ...bridge, which stands 70 feet above the bottom of the gorge. The approach to the bridge on the south side is made by a long, deep cut, which gives a good exposure of the Potomac above the horizon exposed in the gorge. The walls of the latter give the continuation downward of the sandstone seen in the bottom of the cut. This is firm and durable enough to stand with a nearly precipitous face. Some of it has been used in making the piers of the bridge, and although coarse and irregular in composition it has proved quite durable. The lower portion of the walls of the gorge is hidden by talus. The hidden portion is about 12 feet thick. The mass above this to the level of the railroad bed, about 58 feet, is composed of thick layers of hard and coarse sandstone, alternating with more argillaceous and incoherent ones. Many of the harder layers are very coarse and pebbly. The alternating layers vary considerably in thickness, ranging from 3 to 6 feet. Some of the coarser sandstone layers contained rolled subangular masses of gray clay. One fragment embedded in the solid sandstone showed the dimensions 2 by 5 by 7 inches. Numerous small quartz pebbles show themselves on the exposed faces of these layers. The predominant color is gray, but this is often stained rusty-brown or yellowish in patches and irregular layers. The material exposed in the railroad cut illustrates well the great irregularity of the Potomac deposits, making it plain that no single section of an exposure can represent even adjacent parts. Here we see well displayed a characteristic feature in the Potomac sand and sandstone. Any given layer, if traced horizontally, will soon pass into something quite different. This cut is about 80 yards long, its northern end beginning close more

Product details

  • Paperback | 68 pages
  • 189 x 246 x 4mm | 141g
  • United States
  • English
  • black & white illustrations
  • 1236959752
  • 9781236959751