GENERAL FEATURES. 3 



The true character of this formation may he satisfactorily studied in the course of its principal 

 streams, the Pecos and Devil's river. As exposed along the course of these valleys, the 

 view is hounded by steep mural cliffs, composed of limestone, disposed in nearly horizontal 

 strata. This rock exhibits quite a variable texture, its weathered face showing an uniform gray 

 or bluish tint, while its recent fracture has a much lighter color. Owing to its irregular texture, 

 it frequently exhibits a cavernous structure, displaying in its various exposures all the grotesque 

 features of ruined castles, forts, and dilapidated masonry ; examples of which may be seen by 

 reference to numerous sketches. 



The river valleys either expand into more or less extensive alluvial basins, or are completely 

 hemmed in by steep mural faces, forming chasms along their course, to which the Spanish term 

 of canon is generally applied. Thus, in following out the course of valleys in this district, we 

 have a series of basins connected by caiions ; the relative extent of these distinct topographical 

 features being dependent on the local character of the formation, or the varied influence of pre- 

 vious denuding forces. 



The alluvial tracts partake to a great extent in the sterility of tlie plateaus with which they 

 are connected, seldom showing evidence of fertility, and in a great measure destitute of timber 

 growth. 



In the case of the Pecos river, which may be regarded as the main type of streams belonging 

 to this table-laud formation, we observe a contracted but constant body of water coursing through 

 alluvial tracts, or clearing its way through rocky canons. 



In the former case, its tortuous course is marked out between deep banks of earth, so that its 

 turbid waters are for the most part invisible till you come directly on its brink. The average 

 width of the stream, during most of the year, is about 50 feet, and 8 feet in depth. Only limited 

 portions of the adjoining valley are subject to that degree of overflow, such as constitutes what 

 is commonly understood as bottom-land. Owing to the steep and crumbling nature of the 

 banks, travellers often experience no small difficulty in watering their animals ; the water itself, 

 though highly charged with reddish sediment, is not unpalatable. 



In its passase through canons, this stream, like the Eio Grande, cleaves its way between 

 steep walls of rock ; its course during low water being occasionally set off' by lines of sandy or 

 pebbly beach, and forming frequent rapids. 



All the small intermittent streams of this region are copiously bedded with rounded pebbles, 

 derived from the adjoining limestone formation. 



The view from the summit elevations presents not an unbroken table-land, but rather a series 

 of terraces, exhibiting occasionally truncated peaks, and showing a general increasing elevation 

 westward. The mean level is, moreover, marked by depressed valleys, containing dry pebbly 

 beds of streams, and frequently expanding into wide basins. The descent to these valleys is 

 generally abrupt, and is the chief obstacle in the construction of roads, which, with this excep- 

 tion, are marked out with ease, and are unexcelled for purposes of wagon transportation. 



The supply of water over these arid tracts, except in a season of rain, is confined to a few 

 isolated springs, occupying the lower level of some of these depressed valleys, or occasionally 

 bursting out from the base of high rocky ledges. These springs, though generally affording a 

 copious and constant flow of water, are not sufficient to give origin to river tributaries, their 

 issue being quickly absorbed in the lower course of their arid beds. In several of these springs 



