PHYSICAL GEOGRAPHY 711 



Grande flows eastward from the midst of the rugged mountains beyond 

 this scarp, through which it has cut a broad deep notch, the only breach 

 in the mountain barrier throughout its entire length. Between 5 and 15 

 miles south of the Eio Grande the Limon range is fronted by a series of 

 foothills which appear to form the junction between it and the north end 

 of the Sierra de Charagua. The trail through these hills winds along the 

 bottom of wooded quebradas, so that it was not possible to obtain a good 

 view of that portion of the mountains. South of the saddle through 

 which the trail enters the Limon Valley, 4 miles north of Limon, the 

 steep eastern front of the Limon range presents a rather unusual topog- 

 raphy. Half way up the 1,500-foot scarp there projects a series of bench- 

 like secondary ridges which trend at right angles to the axis of the main 

 ridge. These are all very short, are separated from each other by steep, 

 narrow, V-shaped ravines, and terminate abruptly in triangular facets. 

 Either these facets represent the dip slope of very steeply inclined cuestas 

 rising from the floor of the Limon Valley toward the Limon fault or else 

 they are the result of a second parallel fault a short distance east of the 

 major fault-plane. 



Farther to the south, in the vicinity of Rincon and Tatarencla, I had 

 opportunity to penetrate the Sierra de Limon by ascending one of the 

 valleys which notch its eastern front. In that locality the range is mar- 

 gined by steeply inclined cuestas, the dip slopes of which rise from the 

 Limon Valley floor toward the west at high angles. These slopes do not 

 ordinarily continue to the highest summit of the range, but terminate 

 against the fault-scarp, which is here well within the mountains, and 

 beyond which rugged ridges and peaks rise several hundred feet higher 

 to form the crest of the sierra. In places small remnants of what appear 

 to have once been more extensive dip slopes, inclined downward toward 

 the west on the west side of the fault-plane, may be observed high among 

 the summit ridges. 



Sierra de Charagua. — The Sierra de Charagua is a long, narrow, sharp- 

 crested mountain ridge extending in a broadly crescentic curve from a 

 point approximately in latitude 19° 5' south, longitude 63° 22' west to a 

 point in latitude 21° 18' south, longitude 63° 9' west. Throughout the 

 entire distance of 85 miles along the axis of the mountain ridge its width 

 is approximately 4 miles. It is the most easterly of the Front Ranges of 

 the Andes. Both to the north and to the south the other front ranges 

 are distributed en echelon, with each successive range a few miles far- 

 ther to the west than its predecessor in line. Its eastern slope rises ab- 

 ruptly from the margin of the lowlands of eastern Bolivia ; its western 



