Bulletin - United States Geological Survey Volume 260

Bulletin - United States Geological Survey Volume 260

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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. 1905 edition. Excerpt: ... made up largely of nomnagnesian beds, although in its lower part are certain magnesian strata. The thickness of the Platteville averages 55 feet. It ranges from 40 to nearly 70 feet, being greatest toward the eastern part of the region. A generalized section of this formation is as follows: Generalized seetion of Platteville formation. Feet. 4. Limestone and shale 10-20 3. Thin and undulating bedded very fine-grained limestone lTr-25 2. Heavy-bedded magnesian limestone or dolomite 15-25 J. Blue shale 1-5 Bull. 260--05 M 20 The upper member of this section consists of both limestone and shale, commonly in alternating beds, although there is comparatively little uniformity in this respect in different parts of the region. In general it can be said that the shale layers are better developed in the west, while the limestone is more important in the east. The shale beds are usually green or blue, though some of them are white, yellow, chocolate colored, and even black. The chocolate-colored and black shales are highly carbonaceous and are locally termed "oil rock," though the main bed of chocolate-colored shale or the oil rock proper lies just at the base of the Galena. The limestone is commonly a thin-bedded, fine-grained blue rock, which is occasionally subcrystalline and usually nonmagnesian, although it becomes magnesian toward the east. The most marked part of this member of the Platteville is the "glass rock," which is a dense, very fine-grained, hard, conchoidally breaking limestone. It is light chocolate colored when fresh, but quickly weathers to light gray. The shales, and especially the limestones, of this member are rich in fossils, and among these a brachiopod--Dalmanella subceqtiata Conrad--is common. The...show more

Product details

  • Paperback | 244 pages
  • 189 x 246 x 13mm | 440g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236753771
  • 9781236753779