The fifth region comprises the high ridge which divides the basin of the Carilaufquen from Nahuel Huapi, the water of which flows northward toward the Limay and southward toward the Chubut: successive eruptions have covered the surface with lava and ash, which at Añecon rise to a height of 6,700 feet. The granite platform which emerges in the north, at the Cerro Aspero and the Quadradito, rises to a height of 4,400 and 4,700 feet, and in some places presents a bold and rejuvenated aspect. The whole has been cut up in all directions by erosion, and it affords comparatively easy means of getting about, which the Indian tracks have followed. Below the higher slopes the valleys deepen into gorges, and these broaden out in the soft tufa and are lost at the cross-streams of lava or the outcrops of the granite. In so varied a land, with such marked differences of altitude, the winter and summer pastures are always close together. Precipitation is more plentiful than at a distance from the Cordillera; the pasturage is richer, and the size of the flock rises to 1,600 sheep to the league. The sheep pass the winter on the lower slopes, where they are sheltered from the winds and the snow. They descend to the mallin when the dry season sets in and makes the soil firm. In summer they go on to the tablelands, where the pastures extend to a height of 5,000 feet.

Bailey Willis, studying the improvements that might be made in the pastoral processes, concluded that the essential point was to use each pasturage in its best season, and establish a carefully considered rotation on the various lands. This system, which alone would enable them to nurse the natural resources of the scrub in the way of plants for fodder, is used to-day in only a small number of districts—in the east, where the flocks winter on the coastal plain and spend the summer on the Somuncura tableland, and in the west, round the Añecon, where the summer and winter pastures are not far from each other. The custom ought to be general. The area which ought to be reserved for winter pasture comprises the coastal plains, the whole of the low-lying district round Valcheta, and the lower part of the valleys to the south of the Carilaufquen. They are less extensive than the available summer pastures, but their capacity could be enlarged by developing the irrigated areas in the Bajo de Valcheta, and sowing lucerne in the mallinas of the basin of the Carilaufquen. The low valleys round the Carilaufquen ought to be reserved for winter pasture. In the summer the sheep would be taken south to the higher-level valleys, which afford permanent pasture. From there they would spread after the melting of the snow, and after the first rains in autumn, over the high tablelands which surround them.

This plan is obstructed in the first place by the actual terms of ownership, which were imprudently fixed before the examination of the country in detail had been concluded. Thus the Maquinchao ranch, in the lower valley, does not own the upper valley with the summer pastures that ought to belong to it. A more serious obstacle is that it is extremely difficult to remove the sheep. It is not merely roads that are wanting, but a water supply at the various stages.[73]

Between the railway that runs from San Antonio to Lake Nahuel Huapi and the Rio Negro, there is a desert region about seventy miles in width. Red sandstone predominates in it, and it remains uninhabited. North of this travesia the valley of the Rio Negro opens. Its width between Neuquen and Patagones ranges from five to fifteen miles. Its slope diminishes gradually toward the bottom (from 0.67 to 0.49 per 1,000 above Chelfaro; from 0.45 to 0.29 per 1,000 above Conesa).

The sandstone and marl cliffs which enclose it become gradually lower as one goes downward. They dominate the valley at a height of 650 feet at the confluence of the Neuquen, and are only 100 to 130 feet high at Patagones. At the foot of them are broad terraces cut by dissymetrical ravines, in which the beds of sandstone outcrop on the western slope, exposed to the winds, while the eastern slopes are covered with gravel. On the banks of the river there is a strip about two miles wide with abundant herbaceous vegetation between lines of willows. This is covered by the normal floods. The remainder of the river plain, to the foot of the cliffs, has only a thin scrub, with dunes at intervals. Saline clays here overlie the river gravels. The level of the underground water, which is fed by the river, sinks lower as one goes from the banks toward the cliffs. Few parts of the tableland have so desolate an aspect as the bottom of these great Patagonian valleys, when they have not been transformed by irrigation. The pasturage is poor. At Conesa, however, the valley (costa) is used as summer pasture when there is a shortage of water on the surrounding tableland (planeza).

The water-supply is good, the volume of the river ranging from 200 to 900 cubic metres a second. Low water lasts from February to April (end of the summer). From May to July the river has sudden and violent floods—an effect of the autumn rains. The curve sinks again in August and September, to rise once more in October and December, when the snow melts on the Andes. The Limay, the upper basin of which contains large, lacustrine sheets, is more regular than the Neuquen, which has very pronounced low-water, as well as dangerous floods in the autumn. The first attempts at irrigation date from 1885, when the canal of the Roca colony was dug. Others were made lower down at a later date. The co-operative groups organized for the administration of the canals have not been quite as successful as might have been expected. The advance of agricultural colonization has been slow. Costly preparatory work is needed to level the ground and organize the drainage, otherwise saline patches form and spread like leprosy at the expense of the cultivable areas. Lastly, the centre of the valley is exposed to floods.[74]

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