BETWEEN THE PECOS AND DEVIL'S RIVER. 31 



sometimes broken, country. The rocky portions are only exposed along the valleys and water- 

 courses, whose perpendicular walls, now thrown down, appear only as sloping banks. The 

 lithologic nature of the rock becomes more earthy; its fracture, sharper. It, however, frequently 

 presents a rounded and blunt surface, particularly where there is a tendency to disintegration. 

 The limestone embraced in the section of country lying between the mouths of the rivers San 

 Pedro and Las Moras, like that above, seems to be melamorphic ; it, however, differs from the 

 limestone above the river San Pedro, in indications of having been subjected to the action of a 

 higher temperature ; and its cretaceous character is also proved by the occurrence of fossil re- 

 mains, which form in some respects a transition from the adjacent geological zone. The 

 surface of this geological belt is completely covered with drift and alluvial soil ; and the growth 

 of trees (cons'isting almost exclusively of mezquite) appears more liberally distributed. Whilst 

 there are scarcely any trees to be seen upon the prominent points, the dells, basins, or flat 

 valleys, where rain-water washes together and deposits the more fertile portion of the soil, are 

 usually invested with scattered groves of the leguminous trees. 



HOW WATERED. 



The surface of this region is usually dry ; it is, however, well watered, when compared to the 

 country adjacent. 



The road from San Antonio to El Paso del Norte crosses in this belt (about 40 miles wide) six 

 clear and bold running streams, of which Las Moras, Piedras Pintas, Zoquete, and San Felipe 

 are the most characteristic. They are somewhat similar in general appearance, and in all 

 probability have their origin on a more solid but in a greatly deeper situated stratum ; for they 

 pour forth at once their crystal waters either from deep funnel-shaped basins or from rocky clefts. 

 Several of these springs indicate a higher temperature than the water in the streams below. 



The water of all these little streams, as also that of the Eio San Pedro orDevil's river, is 

 strongly impregnated with carbonate of lime. Everything hanging within its touch, or in any 

 way exposed to its action, becomes perfectly coated over by its calcareous deposite in a remarka- 

 bly short time. 



In consequence of the permanence and abundance of running water in these tributaries of the 

 Rio Bravo, their bottom-land will in time be highly valued for agricultural purposes. It would 

 be an easy matter to irrigate it, as the fall of water almost throughout is very considerable. 



INTERSPERSED STRATA. 



The groups of hills mentioned before as placed upon the table-lands of the country between 

 Devil's river and the Pecos, appear again in this belt as belonging not only to the later strata 

 of the cretaceous system, but also apparently to a still later date. These strata are usually met 

 with, bordering and constituting the edges of the different valleys. The fossils occurring in 

 these localities are also of the age just mentioned. As an essential characteristic, we cite here 

 strata and shoals consisting almost solely of entire and fragmentary pieces of Exogyra, Arietina, 

 (Roemer.) They appear either in a state of perfect preservation, or as a real breccia ; the cement 

 of which is mostly an ochre-colored calcareous sand or clay. 



The stratification of this formation shows a succession of layers of variously tinted marls, of 

 more or less coarsely grained sand, and also of differently colored limestone; all are profusely 



