[49] In Brazil the saw-mills for the araucarian pines are established along the São Paolo-Rio Grande Railway.
[50] This anomaly is doubtless due to the proximity of the sea and the respite of the westerly winds in winter. The coast, with its cold waters and the land-winds causing the deeper water to rise, has a special climate of fogs and mists. These, which remind us of the garuas of the coast of Peru, do not penetrate into the interior.
[51] The calcareous flag-stone of La Tosca, which is characteristic of the south-west province of the plain of the Pampa, stretches in the south as far as the Rio Negro in the coast-district. On the other hand, it is almost entirely absent a hundred miles to the west, between the Colorado and the Rio Negro, along the line of the railway from Fortin Uno to Choele Choel.
[52] G. Rovereto, "Studi di geomorfologia argentina: la valle del Rio Negro," Bull. Soc. Geol. Ital., xxxi. 1912, pp. 101-142 and 181-237.
[53] The great mass of the Patagonian Andes differs considerably in geological structure from the Argentinian Andes. The Paleozoic sedimentary rocks and the lofty chains of the pre-Cordillera cease at 36° S. lat. The Mesozoic beds—variegated breccie and porphyritic conglomerates, sandstones, limestones, and marls—which form the western slope of the Andes in central Chile, pass to the eastern slope at 35° S. lat., where they develop in regular folds, in the direction south-south-east, obliquely to the general line of the range. These folds account for the orientation of the interior valleys, which is remarkably uniform from the Rio Negro to the Collon Cura. They pass in the south-west under the sandstones of the tableland. West of this sedimentary zone, the zone of the sub-Andean granites and diorites, which have not been exposed further north except at the base of the western slope, opens out in the Patagonian Andes, of which it is the main body between Lake Lacar and the Gulf of Ultima Esperanza. In fine, the Patagonian Andes are characterised by volcanic formations. They are seen on the eastern slope about 36° S. lat., in the lava-flows and ashes of Payen and Tromen. Further south volcanoes with acid lava and characteristic cones are restricted to the central zone (Lanin, etc.) and the Chilean flank, but flows of fluid basic lava cover enormous stretches at the eastern fringe of the Andes, and they have spread over a good deal of the Patagonian tableland outside the Andean region.
[54] Pablo Groeber, Informe sobra las causas que han producido las crecientes del Rio Colarado en 1914. Dir. Gen. de Minas, Geol. e Hidrol., Bol. No. 11, series B, Geologia (Buenos Aires, 1916).
[55] Most of the lacustrine depressions are continued eastward across the Patagonian tableland in the shape of distinct valleys. The eastern part of the Straits of Magellan is merely a submerged valley on the axis of Otway Water. Useless Bay also is continued eastward by the hollow which ends in the Bay of San Sebastian. Sometimes the waters of the lakes flow eastward, toward the Atlantic, along these valleys. Generally, however, the lakes of the western slope are drained on the west by means of narrow defiles across the Cordillera, or on the north and south by rivers which follow the sub-Andean depression and thread them together in the manner of a rosary. The valley which joins the lake to the Atlantic is in those cases a dead valley, and the inter-oceanic dividing line of the waters is marked by the frontal moraine of the old glacier, which confines the lake on the east. This arrangement is found, with surprising regularity, from the Alumine and the Lacar to the Neuquen, and as far as Lake Buenos Aires and the Seno de la Ultima Esperanza at Santa Cruz. The capture of the waters of the eastern slope by the rivers of the Pacific across the Cordillera is fairly ancient, and certainly pre-glacial. But during the Glacial Period the glaciers obstructed the transverse valleys of the Cordillera, and the waters of the eastern slope found their way to the Atlantic once more. With the retreat of the glaciers the valleys of the Cordillera were successively cleared. The lakes, dammed by the glaciers, were suddenly released and their level lowered. The valleys of the Patagonian tableland were finally abandoned, and the topographical accident of secondary importance, which the ancient frontal moraine of the glacier represents, came to mark the limit of the domain of the Pacific. The freshness of the contours of the dead valleys of Patagonia bears witness to the recent date of this conquest, which was too sudden or rapid to be called a "capture" in the proper sense. It has not been accomplished everywhere. From Lake San Martin to Lake Buenos Aires all the lakes of the eastern slope are drained into the Pacific by rivers which flow into the Culen fiord. But further south, Lakes Viedma and Argentino are still tributaries of the Atlantic. They correspond to the zone of the Patagonian Andes which is still covered by inland ice. To the north, in the basin of the Puelo and the Yelcho, where the trans-Andean valleys long ago ceased to be obstructed by ice, the lakes of the eastern slope which drain toward the Pacific are small in size. Their level to-day is much lower than it used to be, and a network of streams has developed east of them, on the earlier lacustrine region, which is now dry.
[56] Diario de D. Basilio Villarino del reconocimiento que hizo del Rio Negro en el año de 1782 (Coll. de Angelis, vi).
[57] It is Woodbine Parish who corrects Villarino's mistake in confusing the Neuquen, at its confluence with the Limay, with the Rio Diamante, known in the south of the Mendoza province.
[58] Carlos M. Moyano, "Informe sobre un viaje a traves de la Patagonia," Bol. Instit. Geog. Argent., ii. 1881, pp. 1-35.