126 PATAGONIA AND SHEEP-REARING 



William IV Land. The bottom of it is a singular 

 glacial landscape, sown with lagoons, punctuated by 

 scattered hills, with an impermeable soil of drift and 

 mud. From Lake Argentina to Lake Buenos Aires 

 the elevated tablelands, which rise to a height of 5,000 

 feet, back upon the Cordillera, and the sub-Andean 

 depression is interrupted. Similarly, between Lake 

 Buenos Aires and Lake General Paz the contour of the 

 Patagonian tableland is not very marked above the 

 sub-Andean zone. The glacial alluvia at the foot of 

 the Cordillera rise to the level of the tableland, which 

 sinks steadily eastward toward the Genua and the 

 Senguerr. To the north, between Carrenleufu and 

 Lake Nahuel Huapi, the retreat of the lakes has left 

 long narrow beds right in the Cordillera, such as the 

 Valle Nuevo del Bolson, the bed of which has been 

 taken over by the Futaleufu west of the Cerro Situacion. 

 Further east the topographical features of the edge of 

 the tableland (the valleys of the Chubut, Tecka, and 

 Norquineo) lie from north to south. Hence within 

 a space of little more than a hundred kilometres the 

 sub-Andean zone has a series of parallel roads, 

 communicating with each other by means of broad, 

 transverse gaps, which at one time were occupied by 

 the lower lobes of the glaciers. The sub-Andean 

 depression does not go north of Lake Nahuel Huapi. 

 The morphological features of the Patagonian Andes 

 begin at 36° S. lat.^ The edge of the Cordillera, in 



« 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 



