The Principles of Economic Geology (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1918 Excerpt: ...Univ. School of Mines Exper. Sta. Bull. 1, 1913. drift. The distribution of the iron-bearing formation has been determined principally by drilling. The following succession of formations is given bv Leith. Quaternary system: Pleistocene series Glacial drift. Unconformity. Cretaceous system. Unconformity. Algonkian system: Keweenawan series Huronian series: Unconformity. Upper Huronian (Animikie group) Unconformity. Lower-middle Huronian... Unconformity. Archean system: Laurentian series Keewatin series Great basal gabbro (Duluth gabbro) and granite (Embarrass granite), intrusive in all older formations. Acidic and basic intrusive rocks. Virginia slate. Biwabik formation (iron-bearing). Pokegama quartzite. Giants Range granite, intrusive in lower formation. Slate-graywacke-conglomerate f o r mation. Granites and porphyries. Greenstone, green schists, and por-phyries. The oldest rocks of the district are Archean greenstones, green schists, and porphyries of the Keewatin series. These are associated with and probably cut by Laurentian granites and porphyries. The Archean rocks are exposed here and there in the central part of the district. Some but not all of the Archean rocks have a well-developed cleavage which is nearly vertical and strikes about parallel to the axis of the range. The rocks of the Algonkian system rest unconformably upon the Archean rocks and are not so greatly metamorphosed. The oldest member of this system is a sedimentary series of conglomerates, graywackes, and slates, of lower-middle Huronian age. The most extensive exposure is from Eveleth eastward to Biwabik. The lower-middle Huronian beds strike approximately with the axis of the range and stand nearly vertical. Their thickness is probably between 3,000 and 5,000 feet. These rocks a...