The distribution of the dead dunes is connected with the stretches of river sand across the Pampa, which have offered an easy victim to the winds. A line of dead dunes follows the upper course of the Salado in the district of Junin and Bragado. On the line from Buenos Aires to San Luis one crosses it between Chacabuco and Vedia, and then one comes again upon the horizontal plain, which has fresh dunes, only further west, at 120 miles from Villa Mercedes. Its elevation is so conspicuous on the level plain that the first breeders who used its pasturage gave it the emphatic name of the cerillada. D'Azara correctly appreciated the nature of it. "It is," he says, "only a dune of very fine sand." It is only a few yards high. The dead dunes of the Bolivar and Veinte Cinco de Mayo departments, which Parchappe described, have a more conspicuous relief, and in their disposition sometimes remind us of the fresh circular dunes with a central lagoon. The lines of coastal dunes in the eastern part of the Buenos Aires province obstruct the proper flow of the water there, and form a group apart, which must be clearly distinguished from the dunes on the plain.[86]
Thus the impression of monotony which the Pampa makes in us is corrected to some extent by close observation. High and low land alternate on it. Parchappe himself had noticed the contrast between the area that stretches from Buenos Aires to the Salado, with its soft undulations and its well-developed hydrographic network, the horizontal plains on the right bank of the Salado, with their irregular dunes, and the southern plateau of the tosca between the Sierra de Tandil and the Sierra de la Ventana.
We may now distinguish the following regions in the Pampa as a whole:
1. The central part of the Santa Fé province forms what is called the district of the "colonies": that is to say, the domain of the colonies established two generations ago, and the zone in which the type of cultivation introduced by them took root. The chief crops here are wheat and flax. Hedges of service trees (paraisos) surround the fields. In contrast with the parts of the Pampa which have remained naked, the region of the colonies seems a veritable grove. It stretches westward beyond the frontier of the Córdoba province, and it reaches the fringe of the monte between San Francisco and Mar Chiquita. For the north, Miatello gives 30° S. lat. as the normal limit of the wheat-growing area; beyond this it suffers both from the low rainfall of winter and the excessive rainfall in summer. As a matter of fact, the large estates only reach this latitude on the line from San Francisco to Ceres. On the Resistencia line, north of Santa Fé, they stop at 30° 30′ S. lat. In the intervening district the limit of the region of the colonies almost coincides with that of the department of Castellanos, about 30° 45′ S. lat. The area lying between this line and the northern edge of the Pampa is given up to breeding. In the south the region of the colonies stretches as far as Las Bandurias and Irigoyen.
2. South of the region of the colonies, the tableland on the right bank of the Paraná, west of Rosario and San Nicolas, is the maize region, the corn belt of Argentina. Flax is generally cultivated as well as maize. It is the agricultural country par excellence of Argentina. The soil, of fine clay, dark red in colour and retentive of moisture, and the abundant summer rains, are very suitable for maize. The limits of the maize region describe an arc of a circle round Rosario with a radius of 60 to 100 miles. They do not quite reach the frontier of Córdoba in the west, and they leave out the entire south-western corner of the Santa Fé province. The maize belt touches the Paraná between 32° S. lat. and the Baradero. In the north it passes suddenly into the region of the colonies. In the south, on the other hand, there is at the edge of the corn belt an extensive transition-area, where maize and wheat occupy pretty much the same surface; it stretches as far as the Rio Salado de Buenos Aires.
3. The region of the lucerne farms is much larger. It comprises the whole north-west corner of the Buenos Aires province, from the Salado, in the district of Junin, to the southern limit of the Nueve de Julio and Pehuajo departments, and as far as the latitude of Guamini. The limit of the lucerne farms does not include the lands of the central Pampa, but advances westward and takes in part of the Pedernera department in the San Luis province. The lucerne farms run along the San Rafael line to Batavia, and at this point they reach the limits of the colonized zone. In addition, the zone of the lucerne farms includes the whole south-eastern part of the Córdoba province, as high up as the line from Villa Mercedes to Villa Maria, and the southern part of the Santa Fé province. In the whole of this area, fifteen to twenty-five per cent. of the surface is planted with lucerne. The conditions required for its cultivation are a moderate depth of the underground water and a light soil that allows the roots to penetrate easily. The eastern belt of clays is not good for lucerne, which survives there for much less time than in the west, where it may live fifteen or twenty years.
The lucerne belt is above all a great breeding area for horned cattle, as sheep-pasturage injures the lucerne. It is not nearly so monotonous, however, as the preceding regions. In the south-east, in the Buenos Aires province, the creation of the lucerne farms was undertaken at a time when agricultural colonization had already begun. We therefore find two types of exploitation side by side. The cultivation of maize enters it in the south-west, in spite of the comparatively unfavourable climatic conditions. The centre of the lucerne area in the south of the Córdoba province is also a great agricultural zone; but there agriculture is directly connected with the creation of the lucerne estates. It is, in fact, entrusted to colonists who till the ground for four or five years, and restore it to the owners sown with lucerne at the expiration of their lease. The crops consist almost exclusively of wheat and flax. Lastly, in the west (San Luis province and extreme south-west of Córdoba province) the soil gets increasingly more sandy, and the climate drier. A single tillage suffices to destroy the natural vegetation and clear the place for lucerne. The lucerne fields have been created by the breeders themselves, the sole masters of the region, without the aid of the colonists.
4. Beyond the lucerne belt, at the point where the plain rises toward the Sierra de San Luis and the Sierra de Córdoba, the subterranean water sinks deeper. This zone at the foot of the ranges, unsuitable for lucerne, yet with a soil comparatively rich in humus, has been taken up by agricultural workers. The wheat area extends, in the San Luis province, as far as Fraga and Naschel, in the Conlara depression. The maize area extends to Oncativo, in the Córdoba province, between the Tercero and Secundo rivers, where the summer rainfall is heavier. Thanks to the nearness of the mountains, this area has a water-supply for irrigation, and this sustains several small centres of good farms.