Between these and the Cordillera Oriental is an apparently confused mass of broken, intersecting ranges, which on closer examination are found to conform more or less closely to the two outside ranges.
The several ranges of the Cordillera show very different types of structure and were formed at different ages, the Selkirks with their core of pre-Cambrian granite, gneiss and schists coming first, then the Coast Ranges, which seem to have been elevated in Cretaceous times, formed mainly by a great upwelling of granite and diorite as batholiths along the margin of the continent and sedimentary rocks lying as remnants on their flanks; and finally the Rocky Mountains in the Laramie or early Eocene, after the close of the Cretaceous.
From this point the line follows the summits of the Cordillera Silillica north to the Cerro Paquiza, on the Tacna frontier, and to the Nevado Pomarape, near the frontier of Peru.
The Nepena, Casma, Huarmey, Fortaleza and Supe rivers rise on the slope of an outer range called the Cordillera Negra, and are consequently dry during the great part of the year.
The Jurassic and Cretaceous formations, which in the Southern Cordillera are situated outside of the range to the east, form to a considerable extent the mass of the great range, together with quartz porphyry, the Tertiary, granite and other eruptive rocks, which have been observed along all the chain in South America up to Alaska in the north.
The Meta rises on the opposite side of the Cordillera from Bogota, and flows with a sluggish current east-north-east across the llanos to the Orinoco, into which it discharges below the Atures rapids, in lat.
West of the Cordillera Oriental, where special conditions prevail, a great desert plateau stretches entirely across one corner of the republic. Apart from the Andean system there is a group of low, broken, gneiss ranges stretching along the east side of Bolivia among the upper affluents of the Mamore and Guapore, which appear to belong to the older Brazilian orographic system, from which they have been separated by the erosive action of water.
The seven new departments are: Atlantico, taken from the northern extremity of Bolivar; Caldas, the southern part of Antioquia; Galan, the southern districts of Santander, including Charala, Socorro, Velez, and its capital San Gil; Huila, the southern part of Tolima, including the headwaters of the Magdalena and the districts about Neiva and La Plata; Narino, the southern part of Cauca extending from the eastern Cordillera to the Pacific coast; Quesada, a cluster of small, wellpopulated districts north of Bogota formerly belonging to Cundinamarca, including Zipaquira, Guatavita, Ubate and Pacho; and Tundama, the northern part of Boyaca lying on the frontier of Galan in the vicinity of its capital Santa Rosa.
The deeply-indented coast line is filled with islands which preserve the general outline of the continent southward to the Fuegian archipelago, the outside groups forming a continuation of the Cordillera Maritima.
Its course is north and north-west to the Colombian frontier, thence westward and north-west to the Pacific, breaking through the Western Cordillera on its way.