PHYSICAL GEOGRAPHY 707 



W. Schiller: Contrib. al conoc. de la form, petrolif. (Cretaceo) de Bolivia 

 del Sud. Revista del Mus. de la Plata, volume XX, pages 168-197. Buenos 

 Aires, 1913. 



G. Steinmann, H. Hoek, and A. von Bistram : Zur Geologie des sudostrichen 

 Boliviens. Centralblatt fur Min., Geol., und Pal. Stuttgart, 1904. 



Physical Geography 



GENERAL 



The territory between 63 degrees and 64 degrees west longitude and 18 

 degrees and 23 degrees south latitude is occupied by the most easterly 

 ranges of the Cordillera Oriental, or eastern Andes, the foothills border- 

 ing these ranges, the intermontane lowlands which separate them one 

 from the other, and the west margin of the broad interior plains known 

 as the Gran Chaco (see map, figure 1). In general the territory west of 

 63° 30' lies in the Cordilleran physiographic province, while that to the 

 east of this meridian is a part of the Interior Lowlands, but the boundary 

 line between the two provinces is by no means straight; rather, its posi- 

 tion is shifted in different parts of the area studied, from near the sixty- 

 third meridian nearly or quite to the sixty-fourth. 



MOUNTAIN RANGES 



Sierra de Santa Cruz. — The Sierra de Santa Cruz is the front range of 

 the Andes from the eighteenth parallel northward to the latitude of Santa 

 Cruz and beyond for an unknown distance to the northwest, forming a 

 great arc very convex toward the southwest. 4 The rugged heights of this 

 sierra rise to elevations of five or six thousand feet above the sea and are 

 separated by numerous steep-walled canyons, deep carved into resistant 

 sandstones. Its eastern margin is marked by cuestas, inclined eastward 

 at angles of 20 degrees to 40 degrees, composed of massive red beds which 

 dip beneath the sands and clays of the adjacent plain. 



Sierra de Florida. — The Sierra de Florida continues the Andean sys- 

 tem southward from 18° 10' to 18° 35'. Its eastern front is a sheer cliff 

 extending in a general north-south direction for a distance of about 22 

 miles and broken by stream channels only at long intervals. Rugged and 

 forbidding peaks crowd close on each other throughout the region west of 

 this bold escarpment and presumably merge at the western margin of the 

 range into the next mountain group of the Cordillera Oriental. The 

 range itself was not entered; the observations on its geology were marie 

 from the trail which leads southward through Palissa and Florida, paral- 

 leling the mountain front at a distance of 1 or 5 miles. 



* K. C. Heald and K. F. Mather. 1922. 



