SAND HILLS ON THE CHIHUAHUA ROAD. 11 



Oa entering the sand-hills from the north, we first pass over a considerable swell of limestone 

 rock, from the southern slope of which we pass at once into the hills of sand. Its surface, at 

 first variously scattered with arid shrubbery, becomes as we proceed almost pure drifting sand, 

 blown by the wind into varying ripple-marks, and assuming all the different shapes of drift and 

 hollow imaginable. As the view of the surrounding country becomes shut out, there is presented 

 an exact picture of the sandy dunes on an exposed seacoast, and it seems almost strange not to 

 hear the roaring of the surf, or catch a view from the highest elevations of a wide ocean expanse. 



The greatest height of this formation is on the southern side, or in the convexity of the arch, 

 which terminates with a somewhat abrupt face, merging into the shrubby plain below. 



Our route from this point leaves the Chihuahua road, passing more to the west, and thence 

 skirting along the base of jagged mountains, forming a broken range to the south and south- 

 west. The plain traversed is similar in character, and continuous with that on the opposite 

 side of the sand-hills, having, however, an increased elevation. Our route, bearing S.S.W., 

 is interrupted by occasional spurs of limestone rock, proceeding from the adjoining mountains 

 to the south. 



This character continues for some twenty miles, when we begin to notice an obvious change 

 in the external features of the country. The frequent valleys leading from the broken mountain 

 range on our left acquire a more fertile character, and, being removed from the incursions of 

 drifting sand, support a richer growth of plants. Beyond this, the country spreads into wide 

 basin plains, presenting to the eye an uniformly smooth outline. The soil is composed of a stiff 

 clay sediment, and is occupied exclusively with a growth of coarse grasses. In their lower 

 depressions these extended plains frequently present a perfectly bare surface, destitute of all 

 vegetation, the retentive soil either holding the product of recent rains in wide, shallow pools, or 

 more often showing a surface cracked and blistered under the influence of an arid atmosphere. 

 We find frequently scattered over its surface recent land shells, as indications of its lacustrine 

 character. In certain localities these lower depressed flats are covered with a white saline 

 efflorescence, resembling at a distance sheets of water, to the frequent disappointment of the 

 thirsty traveller. The roads leading over these tracts are firm and excellent. The natural 

 supplies of water are very inconstant, being in great measure dependent on rains. 



Our road hence, for a long distance, traverses a succession of these plains, of greater or less 

 extent, alternating with short ridges, occasioned by the passage of an irregular mountain range. 



These ridges present along their line of elevation various depressions, at which the passage is 

 generally accomplished by an easy gravelly slope. The exposed rocks are of carboniferous lime- 

 stone, associated with various igneous products. 



This character of country continues till we reach the first flowing stream yet encountered on 

 our march from the Rio Grande ; this is the Eio Sta. Maria. As here exhibited, it shows a 

 flowing brook of limpid water, from 10 to 2(7 feet in width ; at the crossing knee-deep, and 

 flowing over a pebbly bed. Its source lies far to the south, in the State of Chihuahua; thence 

 flowing north, it empties, about 30 miles from our place of crossing, into Lake Sta. Maria. 

 This lake is shown, by the examination of the boundary commission, to be in close proximity to 

 the larger Lake Guzman, from which it is separated by a range of mountains. 



These lakes, though thus separated, belong to the same general basin, receiving the drainage 

 of a large tract of country— the San Miguel and its tributaries entering on the north, and the 



