This diversity of the physical environment is only fully brought out by colonization. It is colonization, the efforts and attempts of human industry to adjust agricultural or pastoral practices to the natural conditions, which enable us to assign the limits of the natural regions. In this differentiation it is essential to notice the historical element.

The introduction of new crops gives a geographical meaning, which had hitherto escaped observation, to climatological limits such, for instance, as the line of 400 millimetres of rainfall which is the western frontier of the region of cereals. These limits of crops remain uncertain for a time, then experience and tradition gradually fix them. They always keep a certain elasticity, however, advancing or receding according as the market for the particular produce is favourable or unfavourable.

Improvement in the methods of exploiting the soil—the adoption of better agricultural machinery, dry farming, etc.—usually leads to the extension of the sphere of a particular type of colonization, as it enables this type to overcome some natural obstacle which restricted its expansion. Sometimes, however, it brings to light a new obstacle and creates a new geographical limit.

To this category belongs the northern limit of the belt of selective breeding, which slants across the plain of the Pampas from the Sierra de Córdoba to the Paraná. The more or less degenerate cattle of the natives had spread over the whole of the South American continent, except the tropical forests, since the seventeenth century, adapting themselves easily to very different climatic conditions, from the Venezuelan llanos to the sertao of Bahía and the plains of Argentina. But pedigree animals, more valuable and more delicate, introduced on to the Pampas fifty years ago, are not able to resist the malady caused by a parasite called the garrapate. Hence the southern limit of the garrapate suddenly became a most important element in the economic life of the Republic. It would lose its importance if we discovered a serum that would give the animals immunity against Texas fever.

The range of one and the same cause varies infinitely with the circumstances. The limit of the prairie, as of the scrub (monte) which surrounds it on every side, and keeps it at a distance of 320 to 440 miles from Buenos Aires, had no decisive influence on primitive colonization. Whether covered with grasses or brushwood, the plain is equally suitable for extensive breeding. The ranches are the same on both sides of the border. At the end of the nineteenth century, however, when the area of cultivation increased, the prairie was at once found to be superior. The labour required for clearing the brushwood before the plough can work is enough to divert from it, at least for some time, the stream of agricultural colonization. While the population of the monte, wood-cutters and breeders, are indigenous, the prairie has absorbed the immigrants from Europe, and the border of the scrub has become in many places an ethnographical frontier.[2]

THE ARID ANDES. PUNTA VACAS, ON THE TRANS-ANDEAN RAILWAY.

The bottom of the valley is 8,000 feet above sea-level; the sides buried under rubbish. It is especially in this latitude, above a height of 10,600 feet, in the zone where the moisture falls as snow even in summer, that the rock is everywhere buried under its own rubbish. This is Keidel's Schuttzone. It extends to the foot of the Alpine peaks, carved by glaciers.

Photograph by Moody, Buenos Aires.

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