largest in the Andes which has no connection with the river systems on the outer flanks, whether to the east or to the west. There are one or two small ones of a similar kind in the north-west part of the Argentine Confederation. The highlands which surround this great valley (which might be appropriately called the navel of South America) form a continuous re-entering watershed, separating respectively the numerous small rivers flowing into the Pacific, the Amazon system, Avhich drains a large portion of the northern part of South America, and the La Plata system, which drains most of the southern part of the same area. In this region, too, more especially in the eastern Cordillera, it was for a time believed, on the authority of Mr Pentland, that the highest peaks of the Andes were situated; his first estimates were, however, ascertained by himself and others to have been too great. The highest peak is the Nevado de Sorata, close to Lake Titicaca, and estimated at 21,286 feet high; next to it comes the twin peaked Illimani, a little further south, which rises to 21,181 feet. The passes crossing the valley have summits averaging 14,000 feet, but the one which skirts the Nevado do Sorata rises nearly to 16,000 feet above the sea, From about 18 the Andes, like the coast, runs north-west, so that whereas in about 18 S. the crest of the western Cordillera is in 70 W. long., at. 14 S. it has reached a little beyond 75. Here there is another change of direction, this portion of the western Cordillera stretching from about 14 S. to 6 S., the south end being near 75 W., and the north near 80 W., the westing being rather more than half a degree per degree of latitude. From 6 S. to the equator the direction is very slightly to the east of north; beyond this the trend is still more east, so that the termination of the west Cordillera lies between 76 and 78 W. long, in between 7 and 8 N. lat. The northern end of the eastern Cordillera is near 72 W. Returning again, to the Peru vian Andes, we find some lofty peaks which rival, and it may be surpass, those of Bolivia, Thus Sehama is reputed to be 22,000 feet; Chungara somewhat less; Chipicani, 18,898 feet; Arequipa, 18,373; Chuquibamba, 21,000 feet. There are numerous passes over the Andes in Peru, such as those of Gualillos, of the Altos de los Huescos, and of the Altos de Toledo the first mentioned of which rise to 17,820 feet above the sea. North of the Vilcanota Mountains the eastern portion of the Andes is much cut up by the numerous feeders of the Ucayali and Madeira rivers, most of which originate on the flanks of the western Cordillera. At Pasco there is a lofty mountain knot or table-land, which connects the Cordilleras, and at the same time forms the watershed between the upper portions of the basins of the rivers Ucayali, Huallaga, and the Maranon, or Upper Amazon. From this table-land three Cordilleras extend northward, of which the eastern dies out between the Ucayali and Huallaga rivers; the central between the Huallaga and the Upper Amazon; while the western Cordillera is continuous into the mountain knot of Loja, which forms the southern portion of the Andes of Ecuador, and which is estimated to be 11,650 square miles in extent. From this knot two lofty Cordilleras, abounding in volcanoes, both active and extinct, run nearly parallel. They are separated at intervals by transverse ridges into three vast mountain valley plains, of which the two southernmost drain into the Amazon basin, and the northernmost into the basin of the Esmeraldas river. The two Cordilleras are again united in the north by the mountain knot of Los Pastos, on the borders of Ecuador and Columbia. The valley plains are about 40 miles wide. On the south is the valley of Cuenca, which is about 50 miles long, and about 7800 feet above the sea. From it the way into the central valley plain, that of Ambato, is across the transverse ridge by the pass of Assuay, which rises to 15,520 feet, it is about 130 miles long, and about 8000 feet above the sea. The mountain fringe comprises several important volcanoes, viz., Sangay, Tunguragua, and Cotopaxi in the eastern Cordillera ; and the volcano Carguirazo in the western Cordillera, which also includes the lofty Chimborazo, estimated to reach 21,424 feet above the sea. Then crossing over the low transverse ridge of the Alto de Chisinche, we descend into the valley-plain of Quito, which is bordered by one of the most intensely volcanic areas on the globe. To the east are Sinchulagua, Antisana, and Cayambe ; the last is now extinct, stands on the equator, and is 19,534 feet above the sea. It is the highest point on the equator in the globe, and is the only one along that line where perpetual snow exists. In the western Cordillera the prominent eminences are Pichincha and Irnbabura. The valley-plain is about 9500 feet above the sea. Taking Cotopaxi as a centre, Orton observes that the other peaks may be arranged in concentric orbits thus. Runiinaqui and Sinchulagua are 10 miles distant; Iliniza, Corazon, Atacatzo, and Antisana are 25 miles ; Quirotoa, Pichin cha, and Guamani are 30 miles; Llanganati is 40 miles; Tunguragua, Carguirazo, Cayambi, are 50 miles; Chimborazo, Imbabura, and Cotocachi, are 60 miles; Altar is 65 miles; Sangay is 75 miles; lastly, Chiles and Assuay are 100 miles. Chimborazo is the most conspicuous feature in this part of the Andes, and from one point its outline resembles that of a lion at rest, Cotopaxi is the most symmetrical active volcano on the globe. Its apical angle is 122 30 ; and the slope is a little over 30 on the south, west, and east sides, and nearly 27 on the north side. Its summit was attained for the first time on November 27, 1872, by Drs Reiss and Stiibel. The height was found to be about 19,500 feet. Beyond the mountain knot of Los Pastos two Cordilleras run in a north-easterly direction to about 2 N. The western Cordillera is broken by the valley of the Patia, which has its source on the slopes of the valley between the mountain knot of Los Pastos and the transverse ridge south of Popayan. The eastern Cordillera is continued into the Paramo de Guanacas, from which basis the Andes spread out fan-like into three Cordilleras. This paramo, like the cross range between Iliniza and Cotopaxi, forms part of the main watershed between the rivers draining into the Atlantic and Pacific Oceans. North of the paramo this watershed runs along the western Cordillera for some distance, and then crosses several minor ranges of hills with their intervening valleys. The low watersheds at the head of the Atrato basin coincide with it; and north of Cupica Bay it suddenly bends, pass ing from within a few miles of the Pacific to within a few miles of the Atlantic Ocean. Having commenced this general account of the Andes with a notice of the mountain ranges of Columbia, and of the lowlands of the Isthmus of Panama, we thus come round to our starting- point. In the article America there is a brief account of the chain from a geological point of view, as well as of the transverse chains of South America; and under the heads of the various countries through which these pass
further particulars are given.wishes to enter more minutely into this subject: Hum- boldt s works on South America; his papers in the Journal de Physique, vol. liii. p. 30 (1801); another in Gilbert s Annalen, vol. xvi. pp. 394, 450 (1804); Pentland s papers in Phil. Mag., vol. ix. p. 115 (1828), and in the Journal of the Roy. Geoy. Soc., vol. v. p. 30 (1835); papers by Pissis in Comptes Rendus, vol. xl. p. 764 (1855), and vol. lii. p. 1147 (1861), as also in Annales dcs Mines, fifth series, vol. ix. p. 81 (1856); D. Forbes, "On the Geology of
Bolivia and South Peru" in Q. Jour. Geol. Soc., vol. xvii.