Patagonia

Patagonia is the name given to that portion of South America which, to the east of the Andes, lies mainly south of the Rio Negro (41°S), and, to the west of the Andes, south of (42°S). The Chilean portion embraces the southern part of the region of Los Lagos, and the regions of Aysen and Magallanes (excluding the portion of Antarctica claimed by Chile). East of the Andes the Argentine portion of Patagonia is divided into four provinces:

• Neuquen, 42,000 square miles approximately, including the triangle between the rivers Limay and Neuquen, and extending southward to the northern shore of Lake Nahuel-Huapi (41°S) and northward to the Rio Colorado;
• Rio Negro, 76,000 square miles approximately, extending from the Atlantic to the Cordillera of the Andes, to the north of 42°S;
• Chubut, 95,000 square miles approximately, embracing the region between 42° and 46°S; and
• Santa Cruz, which stretches from the last-named parallel as far south as the dividing line with Chile, and between Point Dungeness and the watershed of the Cordillera, an area approximately of 106,000 square miles.

Table of contents

1 Physiography 2 Climate 3 Fauna 4 History

Physiography

The general character of the Argentine portion of Patagonia is for the most part a region of vast steppe-like plains, rising in a succession of abrupt terraces about 100 meters (330 feet) at a time, and covered with an enormous bed of shingle almost bare of vegetation. In the hollows of the plains are ponds or lakes of brackish and fresh water. Towards the Andes the shingle gives place to porphyry, granite, and basalt lavas, animal life becomes more abundant and vegetation more luxuriant, acquiring the characteristics of the flora of the western coast, and consisting principally of southern beech and conifers.

Among the depressions by which the plateau is intersected transversely, the principal are the Gualichu, south of the Rio Negro, the Maquinchau and Balcheta (through which previously flowed the waters of lake Nahuel-Huapi, which now feed the river Limay); the Senguerr, the Deseado. Besides these transverse depressions (some of them marking lines of ancient inter-oceanic communication), there are others which were occupied by more or less extensive lakes, such as the Yagagtoo, Musters, and Colhuapi, and others situated to the south of Puerto Deseado, in the centre of the country. In the central region volcanic eruptions, which have taken part in the formation of the plateau from the Tertiary period down to the present era, cover a large part with basaltic lava-caps; and in the western third more recent glacial deposits appear above the lava. There, in contact with folded Cretaceous rocks, uplifted by the Tertiary granite, erosion, caused principally by the sudden melting and retreat of the ice, aided by tectonic changes, has scooped out a deep longitudinal depression, which generally separates the plateau from the first lofty hills, the ridges generally called the pre-Cordillera, while on the west of these there is a similar longitudinal depression all along the foot of the snowy Andean Cordillera. This latter depression contains the richest and most fertile land of Patagonia.

The geological constitution is in accordance with the orographic physiognomy. The Tertiary plateau, flat on the east, gradually rising on the west, shows Upper Cretaceous caps at its base. First come Lower Cretaceous hills, raised by granite and dioritic rocks, undoubtedly of Tertiary origin, as in some cases these rocks have broken across the Tertiary beds, so rich in mammal remains; then follow, on the west, metamorphic schists of uncertain age; then quartzites appear, resting directly on the primitive granite and gneiss which form the axis of the Cordillela. Porphyritic rocks occur between the schists and the quartzites. The Tertiary deposits are greatly varied in character, and there is considerable difference of opinion concerning the succession and correlation of the beds. They are divided by Wilckensi into the following series (in ascending order)

1. Pyrotherium-Notostylops beds. Of terrestrial origin, contaming remains of mammalia. Eocene and Oligocene.
2. Patagonian Molasse. Partly marine, partly terrestrial. Lower Miocene.
3. Santa Cruz series. Containing remains of mammals. Middle and Upper Miocene.
4. Paranfl series. Sandstones and conglomerates with marine fossils. Pliocene. Confined to the eastern part of the region.

The Upper Cretaceous and Tertiary deposits have revealed a most interesting vertebrate fauna. This, together with the discovery of the perfect cranium of a chelonian of the genus Myolania, which may be said to be almost identical with Myolania oweni of the Pleistocene age in Queensland, forms an evident proof of the connexion between the Australian and South American continents. The Patagonian Myolania belongs to the Upper Chalk, having been found associated with remains of Dinosauria. Other specimens of the interesting fauna of Patagonia, belonging to the Middle Tertiary, are the giganric wingless birds, exceeding in size any hitherto known, and the singular mammal Pyrotherium, also of very large dimensions. In the Tertiary marine formation a considerable number of cetaceans has been discovered. In deposits of much later date, formed when the physiognomy of the country did not differ materially from that of the present time, there have been discovered remains of pampean mammals, such as Glyptodon and Macrauchenia, and in a cave near Last Hope Inlet, a gigantic ground sloth (Grypoiherium listai), an animal which lived contemporaneously with man, and whose skin, well preserved, showed that its extermination was undoubtedly very recent. With the remains of Grypotherium have been found those of the horse (Onoshippidium), which are known only from the lower pampas mud, and of the Arciotherium, which is found, although not in abundance, in even the most modern Pleistocene deposits in the pampas of Buenos Aires. It would not be surprising if this latter animal were still in existence, for footprints, which may be attributed to it, have been observed on the borders of the rivers Tamangoand Pista, affluents of the Las Hefas, which run through the eastern foot-hills of the Cordillera in 47°S.

Glaciers occupy the valleys of the main chain and some of the lateral ridges of the Cordillera, and descend to lakes San Martin, Viedma, Argentino and others in the same locality, strewing them with icebergs. In Patagonia an immense ice-sheet extended to the east of the present Atlantic coast during the first ice age, at the close of the Tertiary epoch, while, during the second glacial age in modern times, the terminal moraines have generally stopped, 30 miles in the north and 50 miles in the south, east of the summit of