PRESIDIO DEL NORTE TO SAN VINCENTE. 



57 



Within this caiion there is rarely a foothold visible along the line of the ordinary water 

 level, and at no place for the whole distance of ten miles would it be practicable to make a safe 

 descent to the v/ater's edge, still less to ascend. The "facile descensus" would here be truly 

 " Averni." 



SECTIONAL VIEW OF THE GKEAT CANON OF THE RIO KRAVO DEL NORTE, NEAR SAN CARLOS. 



i— ^U / 





fc mUcs 



■^=^ 



A. Perpendicular walls of limestone rock, having a gentle dip to the west, giving increased height to the wal E of the caiion, 



along the eastern course of tlie river. 



B. Cross section of the canon, showing the general shape of the chasm. (Same scale, horizontal and perpendicular.) 

 JVo(e.— For 300 read 800. 



It would be barely possible, in a time of high water, to conduct a boat safely through this 

 stupendous chasm. A strong wooden boat, which accomplished the entire distance from El 

 Paso to this place in the service of the survey, being here cast adrift, was found in broken 

 fragments along the river course below. There are rumors among the Mexicans living near 

 here of the attempted passage of this caiion by some daring individuals, but no authentic 

 record of a successful result. 



A perpendicular cross section of this caiion exhibits a rather peculiar feature, at least such as 

 is not noticed elsewhere : thus, instead of a regular slope or perpendicular descent of the canon 

 walls on either side, we have an expansion of the breadth of the caiion at two distinct points, 

 above and below. The vertical cross section would thus correspond to that of a pitcher, showing 

 first a flaring top, then a contraction, and again bulging out below ; the peculiarity consists in 

 this lower expansion, but is evidently susceptible of a ready explanation. Thus, it may be 

 regarded as due to the irregular action of river flood and recession, acting along its pent-up 

 course in such a way as to exert a greater denuding efiect on the sides of the chasm than on its 

 lower bed. 



Professor Hall has suggested that such a shape would be apt to result, in such situations, 

 from the gradual diminution of the body of running water, naturally connected with increasing 

 land elevations. 



The average width of the stream within this caiion is probably about 100 feet ; and when we 

 come to include herein the immense floods that in other places spread out the river overflows 

 for miles, we can appreciate its terrible energy when pent up within such narrow limits. 



Sufficient lias, doubtlessly, been said on this most remarkable feature in the course of the Rio 

 Bravo ; its details, however, will have a general application to what is to succeed, and render a 

 more elaborate notice of the successive canons unnecessary, all of which resemble the above in 

 general aspect, but none equal it in extent and grandeur. 

 8M 



