COLOMBIA 153 Western Cordillera, or Cordillera de Choco, is the least remarkable of the three, and has been worn down in many places into what are comparatively mere rounded hills with easy passages between ; it continues northward, however, much further than the central chain, and in fact extends right through the Isthmus of Panama. O O The llanos or plains of the Orinoco extend eastward from the slopes of the Cordillera de la Suma Paz. As far south as the Vichada they form an almost complete level, destitute of trees, and affording abundant pasturage ; while further south they are covered with forests, display con siderable irregularity of surface, and are not unfrequently broken by steep rocks rising to a height of from 300 to GOO feet. The fundamental formations throughout Colombia are igneous and metamorphic, the great masses of the Cordilleras consisting of gneiss, granite, porphyry, and basalt. In many places the Carboniferous strata have attained considerable development, though they have been thrown into strange confusion by some unknown disturbance. Volcanic forces are still at work, as is shown by occasional earthquakes, and also by such phenomena as those at Batan near Sogamoso, where the subterranean heat is great enough to affect the local climate. Glaciers are still extant in the Paramo del Ruiz, and possibly in some of the other snow-clad heights. The slopes of the various Cordilleras are frequently covered with deep beds of gravel ; and the valleys are full of alluvial deposits of very various periods. The rivers have in many instances cut remarkable passages for themselves through the mountains ; and, according to Codazzi, the Sogamoso has at one time been the outlet of a vast series of lakes which he believed to have occupied the highlands of Bogota, Tunja, and Velez. The rivers of Colombia belong almost entirely to the great Atlantic versant ; but they are distributed by the principal water-shed in very various directions. The two most important are the Magdalena or Rio Grande and the Cauca, which both flow from south to north through nearly the entire length of the country, the former occupying the valley between the Eastern and the Central Cordilleras, and the latter that between the Central and the Western. They unite about 130 miles before reaching the sea, but they so long maintain an independent course that neither can fairly be regarded as a mere tributary of the other. The Magdalena takes its rise in a small lake called the Laguna del Buey or Ox Lake, situated in the plateau of Las Papas. It receives from the right hand the Suaza, the Rio Neiva, the Cabrera, the Prado, the Fuzagasanga, famous for the falls of Tequendama, the Bogota, the Carare, the Opon, the Sagamoso, itself a considerable stream, and the Rio Cesar, a fine river from the Sierra Nevada ; and from the left the La Plata, the Paez, the Saldana, the Cuello, the Guali, the Samana, or Miel, the Nare or Rio Negro, and various minor tributaries. The Magdalena is one of the most important water high ways of the country, in spite of the fact that its current is so rapid as to make thu upward voyage both difficult and tedious. From Honda, where the progress is interrupted by rapids, a native boat takes only about three days to reach the sea, while no fewer than six weeks are spent, even when the water is low. in returning against the stream. Steamers of from 50 to 200 tons burden, how ever, have plied regularly since 1833 between Honda and Barranquilla. The Honda rapids can be surmounted by haulage, and steamers descend them in safety, though there is a fall of 20 feet in two miles, and of 16 feet in the first. Above this point the channel is clear about half-way to the source ; and though the traffic is still mainly carried on by native boats and rafts, a German named Alexander Weckbecker succeeded, in 1875, in taking a large steam boatthe " Moltke " three times to the town of Neiva. The Cauca rises to the west of the source of the Magdaleua, in the Lake of Santiago, in the paramo of Guanacas. In the upper part of its course it flows through a volcanic region, and its waters are so impregnated with sulphuric and other acids that they are destructive of fish. These acids are mainly contributed by the headstream of the Rio Vinagre or Vinegar River, which rises in the Purace volcano. The principal tributaries are the Piendamo. the Ovejas, the Palo, the Amainie, and the La Vieja, froni the Central Cordillera ; and the Jamundi and a large number of minor streams from the Western. After the junction of the Cauca and the Magdalena the united stream attains an imposing breadth ; but it breaks up into several channels before it falls into the sea. The River Atrato, which disembogues in the Gulf of Darien and separates the main branch of the Eastern Cordillera from the isthmian ranges, is of high importance, not only in itself as an actual means of communication, but as affording, in the opinion of many engineers, one of the most feasible means of forming an interoceanic canal. So important was it regarded by Philip II. that its navigation was forbidden in 1730 on pain of death; and the prohibition was not removed for a considerable period. The account, however, so frequently repeated, of the possibility of passing from the Atlantic to the Pacific versant by means of a canal, excavated about 1788 in the Raspadura ravine by some enterprising monk, seems to have little or no founda tion. The Atrato rises in the slopes of the Western Cordillera, has a course of about 300 miles, and a breadth, during the last 96 miles, of from 750 to 1000 feet. Its depth in this lower part of its passage varies from 40 to 70 feet or even more. At Quibdo, 220 miles from the embouchure, it is still 850 feet wide and 8 to 20 feet deep ; and as the fall of the river is only about 3 inches to a mile, steamboats can pass as far as the confluence of the San Pablo and Certigui, 32 miles above Quibd6. Of those rivers that belong to the Orinoco system the most important are the Guaviare, the Meta, and the Vichada. The first is formed of the Guayavero and the Iriwida, which flows from the mountains of Tunahi ; and the principal tributaries of the second are the Chire, the Casanare, and the Lipa. Of those that belong to the Amazon are several tributaries of the Rio Negro branch, and the Caquita, or Japura. This last rises in the eastern slopes of the same table-land which gives birth to the Magdalena and the Cauca ; and its principal affluents are the Pescado, the Caguan, and the Apoponi. Though belonging to Colombia only by its head waters, there is another tributary of the Amazon which bids fair to be of great importance to the country as a means of communica tion with Brazil. This river, the Rio Ia or Potumayo, rises in the Andes in the province of Pasto, under 2 N. lat., has a total length from its source to its confluence of 932 miles, receives in its course 36 affluents, of which several would afford passage for steamboats, and waters a region that abounds in gum elastic, sarsaparilla, cocoa, nut-wood, Pasto resin, gold, and other means of wealth. Its depth is from 7 to 34 feet during low water, and twice as great during flood ; at some places it has a breadth of 1 300 feet, and its current is from 3 to 4 nautical miles an hour. A steamer only takes 10 days to pass from the confluence with the Amazon to the mouth of the Guainue s ; and this place is only 80 or 90 miles from the province of Pasto. The opening up of this route is due to Raphael Reyes, a full account of whose exploration will be found in Petermann s Mittheilungeii for 187G. The only rivers that remain to be noted arc those of the isthmus ; and these are chiefly of importance for their bearing on the question of h teroceanic communication. The principal
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