Patagonia

Patagonia is a geographic region containing the southernmost portion of South America. Located in Argentina and Chile, it comprises the Andes mountains to the west and south, and plateaux and low plains to the east. The name Patagonia comes from the word patagón used by Magellan to describe the native people whom his expedition thought to be giants. It is now believed the Patagons were actually Tehuelches with an average height of 1.80 m (~5’91″) compared to the 1.55 m (~5’09″) average for Spaniards of the time.

To the east of the Andes, it lies north of the Neuquén River and Colorado rivers, and, to the west of the Andes, south of (39°S), excluding the Chiloé Archipelago. East of the Andes the Argentine portion of Patagonia includes the provinces of Neuquén, Río Negro, Chubut, Santa Cruz, and Tierra del Fuego, as well as the southern tips of the provinces of Buenos Aires, Mendoza and La Pampa. The Chilean portion embraces the southern part of the region of Los Lagos, and the regions of Aisén and Magallanes. It excludes those portions of Antarctica claimed by both countries.

Physical geography

Argentine Patagonia is for the most part a region of vast steppe-like plains, rising in a succession of abrupt terraces about 100 metres (330 ft) 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. The high rainfall against the western Andes (Wet Andes) and the low sea surface temperatures offshore give rise to cold and humid air masses, contributing to the ice-fields and glaciers, the largest ice-fields in the Southern hemisphere outside of Antarctica.

Among the depressions by which the plateau is intersected transversely, the principal are the Gualichu, south of the Río Negro, the Maquinchao and Valcheta (through which previously flowed the waters of lake Nahuel Huapi, which now feed the river Limay); the Senguerr (spelled Senguer on most Argentine maps and within the corresponding region), the Deseado River. 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 Colhue Huapi, 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. Lake basins along the Cordillera were also excavated by ice-streams, including Lake Argentino and Lake Fagnano, as well as coastal bays such as Bahía Inútil.

Geology

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 Cordillera. 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):

• Pyrotherium-Notostylops beds. Of terrestrial origin, containing remains of mammalia. Eocene and Oligocene.
• Patagonian Molasse. Partly marine, partly terrestrial. Lower Miocene.
• Santa Cruz series. Containing remains of mammals. Middle and Upper Miocene.
• 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 connection between the Australian and South American continents. The Patagonian Myolania belongs to the Upper Chalk, having been found associated with remains of Dinosauria. One such dinosaur to be found in Patagonia is Argentinosaurus, which may be the largest of all dinosaurs. Other specimens of the interesting fauna of Patagonia, belonging to the Middle Tertiary, are the gigantic 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 Última Esperanza Sound, 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 Andean Cordillera. In general these glaciers flow into lakes towards the East and into Pacific Ocean fjords towards the West. Some of the larger lakes located to the east of the glaciated Cordillera include; General Carrera Lake, Cochrane/Pueyrredón Lake, O’Higgins/San Martín Lake, Lake Viedma, Argentino Lake and many other smaller lakes. In turn, some of these lakes, as is the case with the first three mentioned, drain into the Pacific Ocean through short mountainous rivers, while others, the later two lakes, flow to the Atlantic Ocean through longer and slower moving rivers. These glacial lakes are often strewn with many icebergs. In Patagonia an immense ice-sheet extended to the east of the present Atlantic coast at the close of the Tertiary epoch, while, during more recent glaciation, the terminal moraines have generally stopped, 30 miles (50 km) in the north and 50 miles (80 km) in the south, east of the summit of the Cordillera. These ice-sheets, which scooped out the greater part of the longitudinal depressions, and appear to have rapidly retreated to the point where the glaciers now exist, did not, however, in their retreat fill up with their detritus the fjords of the Cordillera, for these are now occupied by deep lakes on the east, and on the west by the Pacific channels, some of which are as much as 250 fathoms (460 m) in depth, and soundings taken in them show that the fjords are as usual deeper in the vicinity of the mountains than to the west of the islands. Several of the high peaks are still active volcanoes.

Insofar as its main characteristics are concerned, Patagonia seems to be a portion of the Antarctic continent, the permanence of which dates from very recent times, as is evidenced by the apparent recent emergence of the islets around Chiloé, and by the general character of the pampean formation. Some of the promontories of Chiloé are still called huapi, the Araucanian equivalent for “islands”; and this may perhaps be accepted as perpetuating the recollection of the time when they actually were islands. They are composed of caps of shingle, with great, more or less rounded boulders, sand and volcanic ashes, precisely of the same form as occurs on the Patagonian plateau. From an examination of the pampean formation it is evident that in recent times the land of the province of Buenos Aires extended farther to the east, and that the advance of the sea, and the salt water deposits left by it when it retired, forming some of the lowlands which occur on the littoral and in the interior of the pampas, are much more recent phenomena; and certain caps of shingle, derived from rocks of a different class from those of the neighboring hills, which are observed on the Atlantic coasts of the same province, and increase in quantity and size towards the south, seem to indicate that the caps of shingle which now cover such a great part of the Patagonian territory recently extended farther to the east, over land which has now disappeared beneath the sea, while other marine deposits along the same coasts became converted into bays during the subsequent advance of the sea. There are besides, in the neighbourhood of the present coast, deposits of volcanic ashes, and the ocean throws up on its shores blocks of basaltic lava, which in all probability proceed from eruptions of submerged volcanoes now extinct. One fact, however, which apparently demonstrates with greater certainty the existence in recent times of land that is now lost, is the presence of remains of pampean mammals in Pleistocene deposits in the bay of Puerto San Julian and in Santa Cruz. The animals undoubtedly reached these localities from the east; it is not at all probable that they advanced from the north southwards across the plateau intersected at that time by great rivers and covered by the ice-sheet. With the exception of the discoveries at the inlet of Ultima Esperanza, which is in close communication with the Atlantic valley of Río Gallegos, none of these remains have been discovered in the Andean regions.

More about Patagonia here - Map of Patagonia here and also here