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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 Chilo?, and by the general character of the pampean formation. Some of the promontories of Chilo? 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 R?o Gallegos, none of these remains have been discovered in the Andean regions