The climate divides Patagonia into two distinct regions. In the west, the moist Andean zone is suitable for cattle-breeding. About 1870 the Chileans of Valdivia hunted wild cattle in the Nahuel Huapi district. Similarly the Frontier Commission met large herds of wild cattle on the shores of Lake San Martin, which were not yet occupied. Sheep do not get on well in the moist zone, where the rains have washed out the soil and carried away the salts which seem to be indispensable to the sheep. It is the arid tableland that is the land of the sheep. There it has displaced cattle, even in the area which the early breeders at the end of the eighteenth century had filled with cattle. Between the sheep-area and the cattle-area is a mixed region, where the two are combined. It extends more or less according as the transition from a moist to a desert climate is gradual or sudden. It is especially important in the districts where colonization is already old, as in the Fuegian and Neuquen regions. It is lacking in districts where the colonization is recent (Chubut and Santa Cruz), where the sheep-breeders have had a free run as far as the Andes. The ranches of the Cordillera, which specialize in cattle-breeding, all have small flocks of sheep for their own use, their staff being so small that it does not pay to kill the cattle. The sheep-area is by far the more extensive of the two. The patches of agricultural colonization are very scattered and small on its surface. They are restricted to the river-oases of the Rio Negro and the Chubut. These small tilled districts have preserved a remarkable economic independence as regards the pastoral zone, in which they seem lost. Thus the farmers on the Chubut exported their wheat to Buenos Aires until about 1900, and they still send their bales of dry lucerne there. Some of the ranches have tilled small oases in suitable places, but these are merely intended to increase their stores of fodder; not for their flock of sheep, but for the saddle-horses used in watching the estate and the draught-horses used for transport. The pastoral capacity of the Patagonian scrub is, on the average, from 800 to 1,200 head of sheep to 25 square kilometres: less than a tenth that of the prairies of the eastern Pampa. The ranch fixes its residence in the best part of the estate, where there is least fear of a shortage of water, and where pasture is most plentiful. To this the sheep are brought periodically to receive disinfecting baths against the scab, and for shearing. These incessant movements toward the centre of the ranch cause an almost permanent strain on the pasture, and this is one of the chief anxieties of the breeder. The area of the estate is divided as soon as possible into sections (_potreros_) by steel-wire fences, which enables them to watch over the reproduction and improvement of the flock and make the best use of the pasture. Fencing is more advanced near the Cordillera, as timber for the posts is found there.