PRESIDIO DEL NORTE TO THE PECOS. 



55 



At one point on the line of the trail leading round the broken ranges of the mountain ledges, 

 directly bordering the river, to reach its bed some eight miles below the Comanche Ford, the 

 sides of a deep washed ravine bring to view the successive and relative thickness of the various 

 exposures alluded to above. 



We here see the upper members of the cretaceous rocks forming the tabled summits of the 

 adjoining mountains, and marked by frequent cretaceous fossils, resting on a bed of igneous 

 trap-form rock 50 to 80 feet thick, this again overlaying the closer layers of the limestone strata 

 below. 



Our further route, adjoining the river on the Mexican side, passes over high ground, based 

 on limestone rock, and attaining a height of 800 feet or more above the river, the strata here 

 dipping slightly to the west. We again reach the river-bed at the mouth of San Carlos creek, 

 which, draining a considerable valley extending to the south some fifteen miles, affords a con- 

 stant stream of clear water. 



Just below this point commences the gigantic caiion of San Carlos, through which for ten 

 miles the Kio Grande, pursuing a nearly due east course, makes its way. This canon presents 

 unbroken walls of cretaceous limestone. 



The course of the river here cutting the strata in a line directly opposed to the dip, there is a 



FALLS OF HIO BRAVO, NEAR SAN CARLOS. 



constantly increasing elevation of the canon walls. These walls commence with a height of 

 between 200 and 300 feet ; but the fall of the water combined with the rise of the strata, develops, 

 in the course of ten miles, a clear perpendicular height of at least 1,500 feet above the river level. 

 A faint conception only can be formed from these facts of the truly awful character of this 

 chasm. Its course can be marked along the mountain slope in a regular zigzag line, terminatino' 

 by an opening cleft, which rises high and clear above the surrounding mountain ranges. 



