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DESCRIPTION:
SOUTH AMERICA. The early physical history of the South American continent
as recorded in the rocks has been extensively obliterated or greatly
obscured by the events of the development of its later history. The
early land areas are supposed Continent, to be only approximately suggested
by the present exposures of granite and gneisses. The largest of these
old land areas is along the east of the continent, extending with a
few interruptions from the mouth of the Rio de la Plata to within a
short distance of the mouth of the Amazon river. North of the present
Amazon valley and occupying the present highlands of Guiana, north-east
Brazil, and south-east Venezuela was another one of these old land areasa
large island or a group of islands. A chain of islands extended from
the Falkland Islands along what is now the entire west side of the continent.
Upon these ancient shores were laid down the sedimentary beds of the
Cambrian seas. At the close of the Cambrian period the continent was
elevated, many of the former islands were joined together, and the continental
land area was considerably enlarged. The Silurian seas, however, still
covered the basin of the Paraguay, extending from the Serra do Mar on
the Brazilian coast to the axis of the Andes on the west, and covering
at the same time a considerable part of the basin of the Rio So Francisco,
filling the straits between the Andes and the Matto Grosso highlands
and opening east through the region now occupied by the lower Amazon
valley.
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