Bulletin Volume 17-20

Bulletin Volume 17-20

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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. 1919 edition. Excerpt: ...of greenalite. Their shapes differ widely. They are not angular, however. In composition they are like the phase of taconite in which they are embedded. A piece of drill core 2 inches long frequently may contain only one or two pebbles. ALGAL STRUCTURES Algal structures of the Biwabik were first described by Leith as "contorted banding."4 The engineers of the Oliver Iron Mining Company had noticed these peculiar structures at an early date, but Grout and Broderick5 were the first who assigned an organic origin to them. Photographs of outcrops of these structures in their paper show them much better than illustrations of drill cores could. The algal structures found in open pits are shown in Plates VI, B and C. The structures may be recognized by the fine contorted lines which resemble the grain of an especially gnarled and knotty piece of wood. The lines are always thin and according to the way the structures are cut by the drill, they may appear as concentric bands enclosing very irregular cores or form little arches in which the lines converge on both limbs. Mineralogically the structures consist of very narrow red jasper or whitish chert bands which alternate with brown, gray, or black bands. Greenalite structures were not seen with these bands. All of them are surrounded by some cherty phase of tacon1te or conglomerate. Algal structures occur in the lower part of the Biwabik formation from one end of the range to the other without any apparent break, and also in the Upper Cherty division where they were observed as far west as Hibbing. (See PI. II.) Between Chisholm and ITibbing the algal structures of the Upper Cherty division are only locally seen. West of Hibbing they disappear entirely. 3 For illustrations, see Grout and...show more

Product details

  • Paperback | 138 pages
  • 189 x 246 x 8mm | 259g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236899105
  • 9781236899101