Bulletin - United States Geological Survey Volume 399-404

Bulletin - United States Geological Survey Volume 399-404

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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. 1909 edition. Excerpt: ...mantled the limestone, and the ore overlay this, banked against the reefs and filling the pits. Where the reefs and pinnacles of clay-covered limestone are close together the ore is often found to fill solidly the intervening spaces. The ore and limestone drop off abruptly from the hills toward the surrounding valleys. The ancient topography may have resembled in general that of the present, but the old limestone surface was very much serrated, and'faces of isolated crags, now revealed by stripping, show evidences of stream erosion which resulted in the formation oi cliffs. It is of course possible that some of the irregularity of the top surface of the limestone has been produced by solution since the Coastal Plain deposits were laid down, but the evidences of stream erosion and overhanging cliffs are not to be attributed to subterranean decay. These Cambrian limestones have been sharply folded and contorted throughout the district, as shown in the illustration (PI. XIII, B) Overlying the main ore and variegated clays is a massive blanket deposit of Lafayette loam, with a little quartz, chert, and ore gravel. The loam itself is red, and in places is so largely composed of iron oxide in the form of fine sand and loose gravel that it is mined and washed as ore. There are also scattered masses of sandy ore in it close to the surface. The Lafayette is unconformable on the underlying deposits, and its thickness ranges from a few inches to about 15 feet. In places it has been entirely removed by erosion. Ore is mined here by steam shovel from open cuts that require little but stripping, and it is also loosened by pick and shoveled by hand into tram cars. The ore is high enough to be trammed by gravity from most of the cuts to the crusher and...show more

Product details

  • Paperback | 218 pages
  • 189 x 246 x 12mm | 399g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236920503
  • 9781236920508