IO BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
Marfa is 743 miles west from Orange, at an elevation of 4,692 feet, 
with a rainfall of about 19 inches yearly. This lies on a level plateau 
with fine loose soil and with isolated mountain masses, and is a typical 
‘‘short-grass’’ country. Prairie annuals are numerous and abundant 
and Keberlinia and Yucca radiosa are found. Among the annuals are 
Asclepias latifolia, A. tuberosa, Astragalus mollissimus and A. caryocarpus, 
Psoralea linearifolia and P. digitata, Hoffmanseggia jamesu, and Meriolix 
intermedia. 
El] Paso is 939 miles west from Orange, at an elevation of 3,718 feet, 
and receives an annual precipitation of about ro inches. 
The region here includes the valley of the Rio Grande, with its numer- 
ous forms adapted to the dry air and rooting in the alluvium, and Co- 
villea, Sarcobatus, Fouqueria, Croton, many cacti, shrubby composites, 
scattered grasses, and other xerophilous forms on the mesas. 
Of the various separable regions in the transition from the humid to 
the arid areas of the West, that bearing the sotol bears a vegetation of 
marked xerophytic type and is true desert. Since the sotol region is one 
in which the physiographic factor is a determinative one, it is possible 
to delimit it with some accuracy. 
In Texas the main body of the sotol country is embraced in the rough 
limestone region lying between the breaks of the Devil’s River and the 
front ranges of the Cordilleras near Marathon, over 150 miles west, 
extending thence southwestward over the region of the great bend of the 
Rio Grande. Northward, tongues of the sotol formation reach out along 
the divides of the drainage area of the Devil’s River into the Edwards 
Plateau, and of the Pecos River into the Stockton Plateau, and farther 
westward the formation follows the foothills and eastern front of the 
mountains into southern New Mexico. Westward to the Rio Grande at 
Presidio and El Paso the sotol formation occurs wherever the physio- 
graphic features with which it is identified are repeated, viz., débris- 
covered mountain slopes and rolling or hilly areas representing the 
progress of dissection of the plateaus. 
The lechuguilla is almost as widely abundant as the sotol in this 
region, and has been estimated to cover more or less densely an area of 
20,000 square miles. The distance across this sotol-lechuguilla belt 
where it is crossed by the Southern Pacific Railway from east to west. 
is about 150 miles. 
THE SAND-DUNES OF CHIHUAHUA. 
South of El Paso and crossed by the old traders’ trail from the set- 
tlement of Santa Fé to the city of Chihuahua is a long stretch of sand- 
dunes known locally as Los Medanos (supposedly a modification of Los. 
Meganos). Necessarily these were known to the earlier travelers, as. 
evinced by the following apt description by J. R. Bartlett, ‘‘Personal 
Narrative,” etc., 1854). 
