444 



summits of Sotara and Purace, widens consider- 

 ably towards the west, and joins the western 

 chain, which we have called the chain of Cho- 

 co, because the planitiferous land of that pro- 

 vince lies on the slope opposite the Pacific 

 Ocean. By the union of the two chains, the 

 basin of the province of Popayan is shut on the 

 north of Cartago Viejo, and the river of Cauca, 

 in 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 moun- 

 tains, during 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 

 Cali and Cantago, is from 500 to 404 toises ; the 

 latter, from Neiva to Ambalema, is from 265 to 

 150 toises high. It might be said, according to 

 different geological hypotheses, either that the 

 secondary formations were 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 heaped 

 tip on the east and west of the Andes of Quin- 

 diu. The mean difference of this thickness of for- 

 mation, or of these heights, is 300 toises. The 

 rocky ridge of the Angostura of Carare, branches 

 from the south-east, from the counter- fort of 

 Muzo, through which winds the Rio Negro. 



