419 



a simple geometric measure, or by the combined 

 means of barometric, and geometric measures *. 



The Andes, between 33° and 18° of south lati- 

 tude, between the parallels of Valparaiso and 

 Arica, present towards the east three remark- 

 able counter-forts, the Sierra de Cordova, de 

 Salta, and the Nevados de Cochabamba. Tra- 

 vellers partly cross, and partly go along the 

 side of the Sierra de Cordova (between 33° and 

 31° of latitude), in their way from Buenos Ayres 

 to Mendoza ; it may be said to be the most 

 southern promontory which advances in the 

 Pampas, towards the meridian of 65° ; it gives 

 birth to the great river known by the name of 

 Desaguadero of Mendoza, and extends from 

 San Juan de la Frontera and San Juan de la 

 Punta to the town of Cordova. The second 

 counter-fort, the Sierra de Salta and the Jujub 

 of which the greatest breadth is 25° of latitude, 

 widens progressively from the valley of Cata- 

 marca and San Miguel del Tucuman, towards 



* The simultaneous employment of both these means is 

 necessary wherever a base cannot be measured at the level 

 of the sea, or a plan taken from the table-land on which the 

 base has been measured as far as the coast. The want of 

 portable barometers, and ignorance of the use of instruments 

 of reflexion, and artificial horizons, retard the progress of 

 physical geography in the high chains of mountains ; and 

 has been especially prejudicial to the hypsometry of the 

 Andes, and the Rocky Mountains. 



