Geology and mineral resources of Paraguay - a reconnaissance / Геология и полезные ископаемые Парагвая - рекогносцировка

Although this report includes the results of a 6-month reconnaissance investigation of the geology and mineral resources of Paraguay, it is essentially a compilation and interpretation of existing published and unpublished information on the subject.
The rocks can be divided into five major classes, depending on age and mode of origin. The oldest are of Precambrian age, here subdivided into an older group of metamorphic rocks and a younger group of granitic rocks. They are a part of the Brazilian shield and underlie the entire country but are exposed at the surface in only a few places. The second group consists of marine sedimentary rocks and ranges in age from Cambrian or Ordovician through Early Devonian. It comprises three map-pable units, here called the Itapucum! series, the Саасирё series and the Itacurubi series. The third group, which ranges from Pennsylvanian through Triassic in age, constitutes the Gond-wana or Santa Catarina continental clastic sedimentary rocks known in a large part of South America. This group is divisible into three map units—-the Tubarao series of glacial deposits, the Independencia series, and the Misiones sandstone, and, like the marine beds of Paleozoic age, is much thinner in eastern Paraguay than it is in parts of the Gran Chaco in the western half of the country. The fourth group is Tertiary to Recent in age and consists in large part of unconsolidated clay and sand of continental origin. These materials are very thin in most of eastern Paraguay, but they cover nearly all of the Gran Chaco to depths as great as 2,000 feet <...>