S64 



AMAZONIA AND LA PLATA. 



appear to have the meaning of hreach or gap, in reference to the broad opening 

 that occurs between the Sierra del Vulcan and the Sierra de Tandil. 



Farther south the various groups rising north of Bahia Blanca, and commonly 

 called the Ventana Mountains, comprise several parallel ridges disposed in a direc- 

 tion parallel to that of Tandil. In the Ventana range proper the highest summits 

 exceed 3,800 feet ; but they would appear to have formerly attained a far greater 

 elevation. Consisting of whitish quartzites, in many places streaked with red 

 ferruginous oxides, these mountains date from the oldest geological epochs. They 

 existed long before the appearance of the Andes, and were probably at one time 



Fig. 149. — Southern Point of La Vkntana. 

 Scale 1 : 550,000. 





'iei,: ,,,„.''j- J'"'i^^^éij : 



"SÎJJ^S^ip-' 







58' 



\r/esi or Greenwich 



62- 



6145- 



12 Miles. 



amongst the loftiest highlands on the Southern Continent. They are, therefore, 

 to be regarded as mere fragments of enormous masses which have been almost 

 entirely disintegrated by weathering. The valley of the little Rio Sauce Grande, 

 which flows between the Ventana and the Pillahuinco ranges, was formerly a 

 glacial stream. Even still the Ventana receives a little snow every winter. Its 

 name, meaning "Window," has reference to an opening near the summit, through 

 which a peep may be had of the blue sky. The slopes of the sierra are nowhere 

 thickly wooded, and in many places appear quite bare and destitute of all 

 vegetation. 



