BSIOU OF GROOPS. 
313 
of greenstone, plioiiolite, tracTiyte, and ferruginous quartz, 
of whicli the soil of the two slopes is composed, i'rotii 
the ridge of Los Eobles, which separates the table-land ot 
Almae’Ser from the basin of Cauca, the western chain forms, 
first, fn the Cerros dc Carpiiiteria, east of the liio San Juan 
de Micav, the continuation of the Cordillera of Sindagua, 
brohen by the Rio Tatias; then, lowering northward, be- 
tween Cali and Las Juntas de Lagua, and at tlie elevation 
of 800 to 900 toises, it sends out considerable spurs (lat. 
to 5°) towards the source of the Calima, the Tamana, 
and the Andagueda. The two former of tlic.se auriferous 
rivers are tributary streams of the Rio San Juan del Clioco ; 
the second empties its waters into the Atrato. This wideu- 
insr 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 conimumcation 
between the two oceans. The culminant point of this 
system of mountains appears to be the leak ot ioira, 
situated south-east of Novita. 
The northern extremity of this enlargement ot the Cor- 
dillera of Choco, which I have just described, cori-esponds 
with the junction formed on tlie east, between the same 
Cordillera and the central chain that of Quiudui. ihe 
mountains of Aiitioqiiia, on which we have the excellent 
observations of Mr. Restrepo, may be cal ed a knot of 
mountains, and on the uortlierii limit ot the plains of Ruga, 
or tho ba.sin of Cauca, they join the central and western 
chains. The ridge of the eastern CordiUera is at the dis- 
tance of thirty-five leagues from this knot, so that the eon- 
traction of the bed of the Rio Magdalena, between Honda 
and Ambalema, is caused only by the approsiniation of the 
spurs of Mariquita and Guaduas. There is theietoie, 
properly speaking, a group of mountains between a . ^ 
uniting the three chains at once. In the group of the 
province of Autioquia, which forms the ninetion ot the 
central and western Cordilleras we may two 
great masses; one between the 
and the other between the Cauca and the Atrato. The test 
of these masses, which is linked most immediately to the 
snowy summits of Herveo, gives birth on the east to the Kio 
