UNION OF GROCJPS. 313 



of greenstone, phonolite, trachyte, and ferruginous quartz, 

 of which the soil of the two slopes is composed. From 

 the ridge of Los Eobles, which separates the table-land of 

 Almaguer from the basin of Cauca, the western chain forms, 

 first, in the Cerros de Carpinteria, east of the Bio San Juan 

 de Micay, the continuation of the Cordillera of Sindagua, 

 broken by the Rio Patias; then, lowering northward, be- 

 tween Cali and Las Juntas de Dagua, and at the elevation 

 of 800 to 900 toises, it sends out considerable spurs (lat. 

 4 to 5) towards the source of the Calima, the Tamana, 

 and the Andagueda. The two former of these auriferous 

 rivers are tributary streams of the Rio San Juan del Choco ; 

 the second empties its waters into the Atrato. This widen- 

 ing of the western chain forms the mountainous part of 

 Choco: here, between the Tado and Zitara, called also 

 Francisco de Quibdo, lies the isthmus of Raspadura, across 

 which a monk traced a navigable line of communication 

 between the two oceans. The culminant point of this 

 system of mountains appears to be the Peak of Torra, 

 situated south-east of Novita. 



The northern extremity of this enlargement of the Cor- 

 dillera of Choco, which I have just described, corresponds 

 with the junction formed on the east, between the same 

 Cordillera and the central chain, that of Quiudiu. The 

 mountains of Antioquia, on which we have the excellent 

 observations of Mr. Restrepo, may be called a knot of 

 mountains, and on the northern limit of the plains of Buga, 

 or tho basin of Cauca, they join the central and western 

 chains. The ridge of the eastern Cordillera is at the dis- 

 tance of thirty-five leagues from this knot, so that the con- 

 traction of the bed of the Rio Magdalena, between Honda 

 and Ambalema, is caused only by the approximation of the 

 spurs of Mariquita and Guaduas. There is not, therefore, 

 properly speaking, a group of mountains between lat. 5* and 

 5^, uniting the three chains at once. In the group of the 

 province of Antioquia, which forms the junction of the 

 central and western Cordilleras, we may distinguish two 

 great masses ; one between the Magdalena and the Cauca, 

 and the other between the Cauca and the Atrato. The first 

 of these masses, which is linked most immediately to tho 

 snowy summits of Herveo, gives birth on the east to the Rio 



