Lake Carri Lauquen, on the Barrancas (36 deg. 20' S. lat.), which was almost entirely drained in 1914 through the breaking down of the natural dam of soft earth which confined its waters, is not a glacial lake.[54] The chain of glacial lakes stretches from the Alumine to the Seno de la Ultima Esperanza, and is continued southward by Skyring Water, Otway Water, and Useless Bay--genuine lakes in communication with the Pacific by means of narrow channels. The lakes sometimes lie in a narrow and deep glacial valley, the bottom of which they fill; sometimes they branch out into the neighbouring valleys; at other times they advance eastward beyond the zone of the mountains and spread into round basins surrounded by circles of moraines. The largest of them include groups of ramified fiords, which represent their western half, while the eastern half spreads between lower banks.[55] [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