PHYSICAL GEOGRAPHY 709 



The two most prominent peaks in this mountain group are Mount Caro- 

 bana and Mount Cuchilla. The former is a broad dome-shaped elevation 

 with slopes which rise precipitously to a rounded crest, several hundred 

 feet higher than the neighboring summits. Mount Cuchilla is 9 miles 

 farther south, and, as the name implies, is a knife-edge ridge trending 

 northeastward. Its slopes are carved into shelf-like flats and pitches due 

 to the uneven resistance of the nearly horizontal strata of which it is 

 composed. The sky-line formed by it may be seen in the photograph, 

 figure 2. Between these two peaks the rugged sierra displays two deep 

 indentations formed by youthful valleys which lead back into the interior 

 of the range. The more northerly of these canyons is occupied by the 

 upper portion of Eio Florida ; the more southerly by a large tributary to 

 that stream. The Florida flows southeast past the town of the same name, 

 and then swings due eastward out on the plain, and is finally tributary 

 to Eio Grande. 



Sierra de Limon. — South of Mount Cuchilla the Sierra de Florida de- 

 clines rapidly in elevation and in a short distance dwindles to a line of 

 low hills. A few miles farther to the south, in latitude 18° 40', the north- 

 ern outposts of the next mountain range, the Sierra de Limon, appear. 

 These are hogback hills inclined westward and increasing in altitude to- 

 ward the south until they attain mountainous elevations 4 or 5 miles 

 north of the Rio Grande Valley. That portion of the Sierra de Limon 

 which lies north of the nineteenth parallel is the front range of the Andes 

 system and overlooks the interior plain which stretches eastward from its 

 foot. Six to 8 miles east of the Sierra de Limon, approximately on the 

 nineteenth parallel, there are the northern hills of the Sierra de Charagua. 

 •This sierra is the front range throughout its entire length, and its north- 

 ern portion thus overlaps the southern half of the Sierra de Limon, from 

 which it is separated by the Limon Valley. The southern half of the 

 Sierra de Limon overlooks this intermontane lowland and is the second 

 range from the front of the Andes system. 



Throughout its entire extent the Sierra de Limon is a mass of ex- 

 tremely rugged mountains characterized by narrow canyons and sheer 

 precipices which rise to serrate summits. In general these display a close 

 accordance in altitude, estimated at about 5,000 feet above sealevel, and 

 approximately 2,000 feet above the lowland on the east. Toward the 

 north the summit elevations decline regularly until the mountains become 

 low hills due west from Cabezas. The southern termination of the range 

 has not been observed. 



In the vicinity of the Rio Grande the east front of the Sierra de Limon 

 is an almost unbroken fault-scarp rising sheer above the plain. Rio 



