GLACIERS OF PATAGONIA 129 



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. ^ 



Pastoral colonization has now spread over almost 

 the entire surface of Patagonia. The parts that are 

 not yet occupied are of slight extent ; they consist 



' 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 iI^ter-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. 



9 



