South America

SOUTH AMERICA, the southern of the two American continents of the Western Hemisphere, situated between 34° and 82° W. long., and 13° N. and 55° S. lat. It is roughly triangular in shape and in the north-west is joined to the continent of North America (q.v.) by the Isthmus of Panama. South America is the 4th largest of the continents having an approximate area of 7,570,000 sq.m., or about 14% of the land surface of the globe. Its estimated population in 1928 was 74,500,00o, or 9.8 per sq.m. South America lies much farther east in the Atlantic Ocean than North America, the meridional line of New York city cutting it so as to leave 95% of the southern continent lying closer to the Old World. See also AMERICA.

The Coasts.

The South American continent rises abruptly from the ocean floor along nearly all of its coast but the steep ness of the continental margin is more marked on the western side than on the eastern. On the west coast between 5° S. lat. and 35° S. lat. the continental shelf is extremely narrow and is bor dered by abysmal faults (the 3,000-fathom line lies less than 6o m. from the coast-line at Iquique). In this section, and in fact throughout their whole length north of Valparaiso, the Andes, in spite of their great height above the sea, are only the upper por tions of mountains whose bases are thousands of feet below the surface of the Pacific ocean. South of Valparaiso the continental shelf broadens, but it is nowhere of great width and at the en trance to the Strait of Magellan again narrows so that the 1,5oo fathom line is within 15o m. of the coast-line. In general the Pacific coast follows the direction of the Andes. The whole west coast north of the Patagonian archipelago is but little articulated and is completely lacking in good natural harbours. The harbours of Guayaquil and Buenaventura would be exceptions to this rule if it were not that the rivers which empty into them carry so much silt that only constant dredging or carefully engineered dykes to direct the flow and deposit of the silt would make them possible for steamers of deep draught.

From 45° S. lat. to Cape Horn the coastal zone is a broad chain of islands which were probably formed by recent subsidence of a mountainous strip and the consequent invasion of its valleys by the sea. The islands, some of which are very large, are only the higher portions of these mountains that have remained above the sea, while Smyth channel, the Strait of Magellan, and other large channels and sounds are submerged valleys. The channels,

which separate the islands near the mainland and extend back like fiords into the mainland cordilleras, appear to have been greatly over-deepened by the action of the old glaciers. Even to-day great glaciers flow down from the inland ice-fields of the cordil leras to the heads of many of these fiords and, along the Beagle Channel, to the coastline of the channel itself. Many of the larger islands are steep, barren mountain masses which rise to altitudes of 4,000 ft. and in some cases bear glaciers (mostly of the hang ing type, but in some cases long valley glaciers that reach to the sea) on their protected north and north-east slopes.

North of 41° S. lat. the coast belt between the Andes and the ocean averages about 4o m. in width. Its character varies greatly. In southern and central Chile it is occupied by high coast ranges. From 3o° S. lat. to the mouth of the Guayas river it is a sandy arid belt broken by a discontinuous line of coast ranges. Across this arid belt flow streams from the Andes which water narrow, fertile valleys. Few of these streams, however, are perennial; many never reach the sea, and others reach it only in time of flood. North of the mouth of the Guayas river the coastal belt is covered ,with tropical vegetation.

The east coast is in strong contrast with the west. Between Cape San Roque and Sao Paulo the coast to some extent follows the orientation of the eastern border of the Brazilian plateau. On this part of the coast are some of the most beautiful harbours in the world, notably those of Rio de Janeiro, Santos, and Vic toria. These harbours are submerged coastal valleys but the sub sidence which produced them was limited in extent and probably did not affect the whole east coast. In fact in north-eastern Brazil uplift movements have added to the coast a belt of marine depos its. The estuary of the Rio de La Plata is the most marked indentation of the whole South American coast. It is the outlet for the combined waters of the Uruguay and Paraguay river sys tems. South of the La Plata in the Patagonian region many great transverse valleys open to the Atlantic but the recession of the glaciers of the Patagonian Andes, which during the Ice Age were an abundant source of supply, has greatly diminished the streams in many of these valleys. Others, since the recession of the glaciers and the re-opening of old drainage channels through the Andes to the Pacific, are completely dry.