The third zone, 130 miles from the coast, is that of the tableland of the Cerros Colorados, where low masses of red granite rise like an archipelago amongst the Tertiary formations deposited in the intervening depressions. In the west its altitude rises from 650 to 1,300 feet. It is one of the poorest parts of the tableland, and the size of the flock is reduced to 600 head to the square league. The naked rock crops up, not covered, as it is further east, by a bed of gravel. In the valleys there is little water, and it lies very deep. There are no periodical removals of the animals. Winter and summer they remain within range of a few poor springs, which are caused by various outcrops of lava of limited extent; and they leave these, and wander over the tableland, only in the rainy season. Beyond the Cerros Colorados the line rises rapidly, and at Maquinchao it reaches the basin of Lake Carilaufquen. This occupies the bottom of a closed depression, at an altitude of 3,000 feet, dominated on every side by a plateau of lava, toward which, in the south, a number of important valleys run (Nahuel Niyeu, Quetriquile, Maquinchao). These valleys rise in the south in the basalt plateau, at a height of 4,000 and 4,700 feet, and have no running water except at their upper ends. South of Carilaufquen they open upon a broad plain, round which there is a sombre cornice of lava, about 350 feet high. Water has collected on the plain, which consists of alluvial beds redistributed by wind: angular pebbles from the terraces, fine dust from the _mallinas_, and sand from the dunes round the lake. This region is much better than that of the Cerros Colorados. There are many springs at the base of the lava-flows, on the sides of the valleys, and it has as yet not been necessary to look for the subterranean sheets which accompany some of the valleys. The elevated basin of the Quetriquile, though it is only occupied by _intrusos_, seems to have a particularly high pastoral density, and, I am told, feeds 500,000 sheep. In the western part of the region the spring is late, and there is risk of snow during the lambing season. There are, however, no rams there; the lambs are brought from Maquinchao. This arrangement of special zones for the multiplication of the flock enables them rapidly to improve the breed. Here again there are no removals of the animals to a great distance in order to use the pasture. The vegetation of the valleys suffered from the continuous presence of the flocks during the years of drought before 1914; the reproduction of useful grasses was prevented. There is, however, less danger here than on the Cerros Colorados, because the _mallinas_ are extensive, and they suffice for feeding the sheep during the periods when the _manantiales_ of the tableland dry up, and the animals are confined to the valleys.