Text-Book of Geology Volume 3

Text-Book of Geology Volume 3

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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. 1902 edition. Excerpt: ...to light as serves to characterize a series of deposits at the base of the Palaeozoic formations. This assemblage of fossils, Barrande's first or Primordial fauna, is now by common consent more commonly known as Cambrian. The use of the terms Cambrian and Silurian will be more fully referred to in later pages. Rocks.--The rocks of the Cambrian system present considerable uniformity of lithological character over the globe. They consist of gray and reddish grits or graywackes, quartzites and conglomerates, with shales, slates, phyllites or schists, and sometimes thick masses of limestone. Their false-bedding, ripple-marks, and sun-cracks indicate deposit in shallow water and occasional exposure of littoral surfaces to desiccation. Sir A. C. Ramsay suggested that the nonfossiliferous red strata may have been laid down in inland basins, and he speculated upon the probability even of glacial action in Cambrian time in Britain.' As might be ex pected from their high antiquity, and consequent exposure to the terrestrial changes of a long succession of geological periods, Cambrian rocks are usually much disturbed. They have often been thrown into plications, dislocated, placed on end, cleaved, and metamorphosed. In Wales they include toward their base an interesting volcanic group consisting of felsitic and diabase-tuffs, and olivine-diabase in interbedded 8 Q. J. Geo!. Soc. xxvii. 1871, p. 250; Proc. Koy. Soc. xxiii. 1874, p. 334; Brit. Assoc. 1880, Presidential Address. sheets, through which eruptive acid rocks (quartz-felsites, etc.) have risen. Life.--Much interest necessarily attaches to Cambrian fossils, for excepting the few and obscure organic remains obtained from pre-Cambrian strata, they are the oldest assemblage of organisms yet...show more

Product details

  • Paperback | 150 pages
  • 189 x 246 x 8mm | 281g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236881923
  • 9781236881922