THE CENTRAL CHAIN. 311 



towards the province of Antioquia. In 5 15' of latitude, 

 this chain, the only one that shews traces of recent vol- 

 canic fire, in the summits of Sotara and Purace, widens 

 considerably towards the west, and joins the western chain, 

 which we have called the chain of Choco, because the pla- 

 tiniferous land of that province lies on the slope opposite 

 the Pacific ocean. By the union of the two chains, the 

 basin of the province of Popayan is close on the north of 

 Cartago Viejo ; and the river of Cauca, issuing from the 

 plain of Buga, is forced, from the Salto de San Antonio, to 

 La Boca del Espiritu Santo, to open its way across the 

 mountains, along a course of from 40 to 50 leagues. The 

 difference of the level is very remarkable in the bottom of 

 the two parallel basins of Cauca and Magdalena. The 

 former, between Call and Cantago, is from 500 to 404 

 toises ; the latter, from Neiva to Ambalema, is from 265 to 

 150 toises high. According to different geological hypo- 

 theses, it may be said either that the secondary formations 

 have not accumulated to the same thickness between the 

 eastern and central, as between the central and western 

 chains ; or, that the deposits have been made on the base of 

 primitive rocks, unequally upheaved on the east and west of 

 the Andes of Quindiu. The average difference of the thick- 

 ness of these formations is 300 toises. The rocky ridge of 

 the Angostura of Carare branches from the south-east, from 

 the spur of Muzo, through which winds the E-io Negro. By 

 this spur, and by those that come from the west, the eastern 

 and central chains approach between Nares, Honda, and 

 Mendales. In fact, the bed of the Rio Magdalena is nar- 

 rowed in 5 and 5 18', on the east by the mountains of 

 Sergento, and on the west by the spurs that are linked with 

 the granitic mountains of Maraquito and Santa Ana. 

 This narrowing of the bed of the river is in the same 

 parallel with that of the Cauca, near the Salto de S;:n 

 Antonio; but, in the knot of the mountains of Antioquia 

 the central and western chains join each other, while between 

 Honda and Mendales, the tops of the central and eastern 

 chains are so far removed, that it is only the spurs of each 

 system that draw near and are confounded together. It is 

 also worthy of remark, that the central Cordillera of New 

 Greuada displays the loftiest summit of the Andes in the 



