GENERAL DESCRIPTION OF THE COUNTRY. 45 



It "v^as not in my power to explore this range to the south, hut I was informed hy persons worthy 

 of confidence, that throughout its whole extent, as far south as the parallel of Mazatlan, it was 

 utterly impassable for wagons, and there was no possibility of finding, south of 31° 20', a line 

 for a railway. The report of its impracticability for wagons was confirmed by the fact that 

 the Camino real, (highway,) established by the Spaniards to connect Chihuahua and Guymas, 

 makes a great circuit, and passes to the north of 31^.20, and within what is now the territory 

 of the United States. 



This stupendous range of mountains, which drops so abruptly a few miles north of the bound- 

 ary, as if to make room for the highway which is to connect the Pacific and Atlantic States, no 

 doubt, reappears to the north, in the neighborhood of the Grila, but our information is not yet 

 sufficient to establish the connexion. I am quite satisfied of one thing, however ; its equivalent 

 is not to be found in what is called the Sierra Madre, in ISTew Mexico, 



Pursuing our course still eastward, we pass over wide plains bounded by detached ranges of 

 mountains of metamorphic and other limestones^ associated with igneous rocks, rich in silver 

 and lead, and at El Paso we encounter the western flank of the third great mountain chain, 

 the Rocky mountains, known in that particular locality as the Organ mountains ; and at inter- 

 vals of about eighty miles we cross two other ranges, the Eagle Spring mountains and the 

 Limpia range of mountains. 



■ 



The view will give a very good idea of the appearance of the Organ mountains in the distance, 

 and of the Great Mesa, which reaches far away to the west. It is from the bed of the Eio Bravo, 

 just above the gorge, where the river breaks through the range at El Paso. 



These three chains of mountains appear to be spurs of the Rocky mountains, and are character- 

 ized by the presence of carboniferous limestone, greatly disturbed by igneous protrusions of what 

 Professor Hall characterizes as of ^^comparatively modern origin/' 



And throughout this whole region, the carboniferous and metamorphic limestone is not 

 unfrequently traversed by rich seams of argentiferous lead ore. Between the San Luis range 

 and the Organ mountains, the first of the Rocky mountain range, the metamorphism of the 



m 



rocks is so complete and the irruptive lines so freq^uent, and protrusion above the crust of the 

 earth so detached, it is impossible to say, with our present information, where the one begins or 

 the other ends, or whether they do not all belong to the same system. 



It is between these two ranges, upon the banks of the Janos river, that we discover the first 

 evidences from the west of that vast cretaceous formation "which has been traced from the 108th 

 to the 101st meridian of longitude, and as far north as the Great Salt Lake, and south to the 

 25th parallel of longitude. 



The western limit of this formation, discovered by the boundary survey, is the basin of the 

 Janos river in Chihuahua, and its easternmost limit San Antonio, in Texas. How far it extends 

 north and south has never been ascertained, but it has been traced in one direction as far as the 

 Big Salt Lake of Utah Territory. 



Granite, and its associated gold-bearing rocks, occur sporadically throughout the Rocky 

 mountain chain, and its spurs ; but the distinguishing feature, in an economical point of view, 

 is the prevalence of carboniferous limestone, with which is found associated argentiferous 

 galena. 



Silver mines of richness have been discovered, and some of them worked to a limited extent, 

 in the mountains about Tucson, at Barrancas, Presidio del Norte, Wild Rose Pass, in the Organ 



mountains, and other localities, accounts of which will be found efsewhere. 



