The limits of the prairie—The rains—The wind and the formation of the clay of the Pampas—The wind and the contour—The zones of colonization on the Pampas—Hunting wild cattle and primitive breeding—The sheep-farms—The ranches—The region of "colonies"—The region of lucerne, maize, and wheat—The combination of agriculture and breeding—The economic mechanism of colonization—The exchanges between the different zones of the Pampas.
The Pampean landscape is doubtless one of the most uniform in the world. Its monotony is tiring to the eye; it is partly responsible for the mediocrity of most of the descriptions of the Pampas. But this uniformity is an advantage for the purpose of colonization. Attention has often been drawn to the rapidity with which plants and animals introduced by Europeans spread in the Buenos Aires district, and, pushing ahead of the breeders and farmers, colonized the Pampas. In the second half of the nineteenth century, when the whole extent of the plain beyond the ancient Indian frontier was occupied, the development of it was so much easier because it was possible to use simpler and more uniform methods of exploitation. It needed neither large capital nor long personal experience on the part of the immigrant. Basques and Italians who had only just landed could take an active part in it almost without apprenticeship. The primitive groups of population could advance from one zone of the plain to another and take with them their own methods of farming and breeding, their own form of rural economy.
A close study will, however, enable us to detect appreciable physical differences in the Pampean plain. Neither climate nor soil is the same all over it.
The name "Pampa" chiefly means a vegetal growth, a prairie. Its limits are the frontier of the scrub (monte), and strange as it may seem, it is still difficult to trace them exactly. North of Santa Fé, between the Salado and the Paraná, the Pampa stretches as far as Fives-Lille, a little beyond 30° S. lat.[76] On the Central Norte and the Central Argentine lines the fringe of the monte reaches to Fuertin Inca and Malbran, about 170 miles north-west of Santa Fé. It then turns south-east and south, passing round the entire depression of Los Porongos and Mar Chiquita; and the line from Santa Fé to Córdoba crosses it at Francia and approaches the Rio Secundo. South of the Rio Secundo it goes westward and joins the foot of the Sierra de Córdoba south of the Rio Tercero (at the stream Tequia). From this point to La Cambre, some sixteen miles east of San Luis, the prairie extends as far as the edge of the sierras, and penetrates into the southern half of the Conlara depression, between the hills of Córdoba and of San Luis (Pampa de Naschel). The mimosa forest enters the steppe in narrow belts along the Rio Quinto to within a few leagues below Villa Mercedes, along the Rio Tercero as far as the confluence of the Saladillo, and along the Salado to the south of Santa Fé. There are, in addition, many isolated clumps of chañares and more extensive patches of wood in the north-west corner of the prairie (Santa Fé province). The monte along the Salado is continued south of Santa Fé along the Paraná, as far as the point where the chief arm of the river reaches the cliffs on the right bank, at San Lorenzo. This is the domain of the ombu, a tree with thick trunk and naked roots which is found scattered over the prairie in the Paraná region as far as south of Buenos Aires.
In the west, between San Luis and the mouth of the Colorado, the transition from the Pampa to the monte is gradual. Just as at Santa Fé, the approach of the monte is announced by the appearance of chañares, in the south-west corner of the Córdoba province and on the southern slope of the Sierra de la Ventana. The monte, properly so called, though impoverished, invaded by the jarilla, and mainly composed (as in northern Patagonia) of dwarf mimosas, covers the area of the Pampean sierras on the left bank of the Chadi Leuvu and the Colorado. Between this area and a line passing through Rancul, Anguil, Atreuco, and Bernasconi, where the naked prairie begins, there is a mixed zone which one may call the calden zone. This mimosa, a near relative of the algarroba, which has a wider range than the other plants of the monte in this latitude, forms woods at intervals in the south of the San Luis province and on the flanks of the parallel valleys of the central Pampa. Between these woods the tableland is generally covered by the prairie, with occasional patches of chañares. About twenty-five miles east of Buena Esperanza the line from San Rafael touches the far corner of a forest of caldenes, which stretches south-westward, and reaches the Rio Salado about 35° 30′ S. lat. Beyond Buena Esperanza it keeps on the prairie as far as the crossing of the Salado, which here marks the limit of the monte. The Rio Negro line passes directly from the prairie to the Patagonian scrub mid-way between Bahía Blanca and the Colorado.
Within these limits the prairie extends without a break. The sierras of the Buenos Aires province have no arborescent vegetation.
The zone of the prairie, intermediate between tropical Argentina and the sub-desert regions of western Patagonia, has a medium rainfall. It decreases gradually from north-east to south-west. There is a rainfall of 1,200 to 1,000 millimetres on the lower Paraná, and only 400 to 600 millimetres on the western edge of the Pampa. The zone which lies between the 800 millimetres and 600 millimetres average is more than 270 miles in breadth. But what is most characteristic of the climate of the Pampa is the equal distribution of the rain throughout the year, and the absence of a real dry season. In this the Pampa differs from the surrounding regions, both in the south-west and the north. At Buenos Aires the six months of the (relatively) dry season yield, nevertheless, 44 per cent. of the total rainfall, and at Bahía Blanca 40 per cent. This regularity diminishes in proportion as one approaches the coast. At Rosario the six months of the dry season only yield 30 per cent. of the year's rain; at Villa Mercedes (San Luis province) 25 per cent. When one goes beyond the limits of the prairies the ratio of rain in the dry season decreases rapidly; it is only 20 per cent. at Córdoba and 18 per cent. at San Luis. At Córdoba, the curve of the rainfall indicates a typical tropical regime, with a summer maximum and a very low minimum in winter. Passing south-eastward from Córdoba, at Bellville, Villa Maria and especially Rosario, the dryness of the winter diminishes, and at the same time a secondary minimum appears in the middle of summer (January-February). At Buenos Aires, the form of the curve changes completely. The summer minimum is almost as low as the winter minimum, and most of the rainfall is in the spring (September) and the beginning of the autumn (March).[77]