The apparently uniform level of the pampas is much broken along its southern margin by the Tandil and Ventana sierras, and by ranges of hills and low mountains in the southern and western parts of the territory of La Pampa.
Other small rivers rising in the Cordoba sierras are the Primero and Segundo, which flow into the lagoons of north-east Cordoba, and the Quinto, which flows south-easterly into the lagoons and morasses of southern Cordoba.
The Cordillera, which bounds them on the west, is formed of folded beds, while the Sierras which rise in their midst, consist mainly of gneiss, granite and schist.
In the western Sierras, which are more or less closely attached to the main chain of the Cordillera, Cambrian and Silurian fossils have been found at several places.
Besides the rivers mentioned, the chief streams are the Santa Lucia, which falls into the Plata a little west of Montevideo; the Queguay, in Paysandu; and the Cebollati, rising in the sierras in Minas and flowing into Lake Mirim.
None of the sierras or mountains in Uruguay exceeds (or perhaps even attains) a height of 2000 ft.; but, contrasting in their tawny colour with the grassy undulating plains, they loom high and are often picturesque.
Mining attracts much attention in the sierras, and its mineral deposits are rich.
A small part bordering the Venezuelan sierras is elevated and mountainous, but the greater part forms an immense alluvial plain, densely wooded, traversed by innumerable rivers, and subjected to extensive annual inundations.
When the Orinoco is reached its lower basin is contracted between the Guiana highlands and the northern sierras, and its tributaries begin to come in more nearly at right angles, showing that the margins of the actual valley are nearer and higher.
The surface again rises into mountain ranges, which include the Parima and Pacaraima sierras on and adjacent to the Brazilian frontier, with a number of short spurs reaching northward toward the Orinoco, such as the Mapichi, Maraguaca, Maigualida, Matos, Rincote and Usupamo.
Some of the culminating points in these ranges are the Cerros Yaparana (7175 ft.) and Duida (8120 ft.) in the Parima sierras near the upper Orinoco, the Sierra de Maraguaca (8228 ft.), and the celebrated flat-topped Mt Roraima (8530 ft.) in the Pacaraima sierras on the boundary line with Brazil and British Guiana.
The Orinoco is supposed to have 436 tributaries, of which, among the largest, the Caroni-Paragua, Aro, Caura, Cuchivero, Suapure, Sipapo and Ventuari have their sources in the Guiana highlands; the Suata, Manapere and Guaritico in the northern sierras; and the Apure, Uricana, Arauca, Capanaparo, Meta, Vichada and Guaviare (the last three being Colombian rivers) in the llanos and Andes.
The Apure receives two large tributaries from the northern sierras - the Guarico and Portuguesa.
South of the sierras, however, the climate is much drier and hotter.
Families, the former inhabiting the regions northward of Cuzo, and the latter occupying the Titicaca basin and the sierras of Bolivia.
In the sierras they have the same general occupations, but there are no social bars to their advancement, and they become lawyers, physicians, priests, merchants, officials and capitalists.
Potatoes are grown everywhere in the sierras, and with quinua are the only crops that can be raised for human food above 13,000 ft.
There are good pastures in the sierras, and cattle have been successfully reared in some of the departments since the early years of Spanish occupation, chiefly in Ancachs, Cajamarca, Junin, Ayacucho, Puno, and some parts of Cuzco.
The labourers are commonly obtained from the Cholos, or Indian inhabitants of the sierras, who are accustomed to high altitudes, and are generally efficient and trustworthy.
Pop. 8000 in 1896), on the Rio Santa or Huaraz, is a large mining centre in the sierras, 9931 ft.
The principal right-hand tributaries, besides the Gallo and Zezere, are the Jarama, descending from the tableland of New Castile a little below Aranjuez, the Alberche and the Tietar, which collect their head waters from opposite sides of the Sierra de Gredos, and the Alagon, from the rough and broken country between the Sierras de Gredos and Gata.
ALPUJARRAS, or [[Alpuxarras, The]] (Moorish al Busherat, " the grass-land"), a mountainous district of southern Spain, in the province of Granada, consisting principally of valleys which descend at right angles from the crest of the Sierra Nevada on the north, to the Sierras Almijara, Contraviesa and Gador, which sever it from the Mediterranean Sea, on the south.
At the highest point of the transisthmian railway), but their general elevation is much lower, and they are broken by wooded sierras and eroded by water-courses.
These sierras lying near the coast have an imposing appearance from the lowlands, but when seen from the plateau their general elevation is so dwarfed as to render them comparatively inconspicuous.
The lowland or tierra caliente region, which lies between the sierras and coast on both sides of Mexico, consists of a sandy zone of varying width along the shore-line, which is practically a tidewater plain broken by inland channels and lagoons, and a higher belt of land rising to an elevation of about 3000 ft.
The principal watershed is formed by the sierras of the state of Mexico, from which streams flow north-east to the Gulf of Mexico, northwest to the Pacific and south-west to the same coast below its great eastward curve.
The largest rivers of Mexico are: the Rio Grande de Santiago, called the Lerma above Lake Chapala, rising in the state of Mexico and flowing westward across Guanajuato, Jalisco and Tepic to the Pacific coast, with a total length of 540 m., celebrated for its deep canyons and waterfalls; the Rio de las Balsas, or Mescala, which rises in Tlaxcala and flows south and west to the Pacific with a course of 426 m.; the Yaqui, which rises in western Chihuahua and, after breaking through the northern ranges of the Sierra Madre Occidental, flows south-westerly across Sonora to the Gulf of California, with a length of 390 m.; the Grijalva, also called the Chiapas on its upper course, which has its sources in the state of Chiapas and flows north-west and north across Tabasco to the Gulf of Mexico, with a total length of 350 m.; the Fuerte, which rises in southern Chihuahua and, after breaking through the sierras, flows south-west across Sinaloa to the Gulf of California, with a course of 340 m.; the Usumacinta, which is formed by the confluence of the Chixoy and Pasion on the east frontier of Chiapas, and flows north-west across Tabasco to the Grijalva, with a course of 330 m.; and the Panuco, which has its source in the north-west of the state of Mexico and flows north-eastward to the Gulf of Mexico.
Nearly all the Gulf coast rivers, however, are obstructed by bars owing to the quantity of silt brought down from the sierras and the prevailing winds and currents on the coast.
On the lower terraces of Michoacan are Patzcuaro and Cuitzeo lakes, and elsewhere among the sierras are numerous other small bodies of water.
Deeply into the:tropical half of the country, carry with them temperate and sub-tropical conditions over much the greater part of the republic. Above the plateau rise the marginal sierras, while a few isolated peaks in the region of perpetual snow give to Mexico a considerable area of cold temperate and a trace of arctic conditions.
In the sierras, above the tierras frias, which are not " cold lands " at all, are the colder climates of the temperate zone, suitable for cereals, grazing and forest industries, and, farther up, the isolated peaks which rise into the regions of snow and ice.
On the Spanish side, from north to south, are (1) the zone of Mont Perdu, Upper Cretaceous and Eocene; (2) the zone of Aragon, Eocene; and (3) the zone of the Sierras, Trias, Cretaceous and Eocene.
The rough country between contains the following so-called " ` Sierras," which are not really ranges: in Veragua province, Sierra de Veragua, with Santiago (9275 ft.) near the Chiriqui range, and Santa Maria (4600 ft.), immediately north of the city of Santa Fe; in Los Santos province (Azuero Peninsula), bold hills rising 3000 ft., and in Panama province, the much-broken Sierra de Panama, which has a maximum height of 1700 ft.
In places this strip nearly disappears, the sierras rising almost immediately from the seashore.
Of the city of Oaxaca in a knot of sierras, San Felipe del Agua (10,253 ft.) standing on the eastern margin of the beautiful Oaxaca Valley, and the Cerro del Leone, southwest of Tehuantepec, the highest summit in the Sierra Madre del Sur.
Between Guajara-Merim and this fall, inclusive, the Madeira receives the drainage of the northeastern slopes of the Andes, from Santa Cruz de la Sierra to Cuzco, the whole of the south-western slope of Brazilian Matto Grosso, and the northern one of the Chiquitos sierras, an area about Scale, z:2z,50o.000 English Miles 0 5 o zoo 200 390 equal to that of France and Spain.
The chief sierras, or ranges, are those of Maria, in the north; Estancias and Oria, north of the Almanzora river; Filabres, in the middle of the province; Cabrera and Gata, along the southeast coast; Alhamilla, east of the city of Almeria; Gador in the south-west; and, in the west, some outlying ridges of the Sierra Nevada.
By a detached group of low sierras known collectively under the name Chiquitos, which belong to the Brazilian highlands rather than to the Andes.
De Chiquitos, adjacent to the sierras of that name, have long been used for this purpose.
While the supply had been furnished by a private corporation, the city was in 1910 planning for the ownership of its water-system, the supply to be drawn from the Sierras at a cost of some $45,000,000.
The electric power and light are drawn from the Sierras, 140 m.
They are known as the Sierras de Chiquitos, and are geologically interesting because of their proximity to the eastern projection of the Andes.