TO JUNCTION OF GUAM) AND GKEEN RIVERS. 37 



value, as regards the determination of doubtful points in the geology of this region. 

 It must be confessed, however, that many questions are left unsettled which we had 

 hoped to Bolve, and I am convinced that there are few localities within the Held of the 

 American geologisl where patient and accurate investigation would be bo likely to 

 result in the discovery of facts of high scientific value as in that under consideration. 



SANTA FE MOUNTAINS. 



As I have mentioned in my former report, the great mass of the Santa Fe Mount 

 ains is composed of coarse, red, feldspathic granite, which , if not peculiar to, is at least 



highly characteristic of, many of the mountain ranges of the central portion of the con- 

 tinent included in what is known as the Rocky Mountain system. As we shall see 

 further on, a granite to the eye identical with this forms the eon: or axis of the Nasci- 

 miento Mountain, the Sierra de la Plata, and other of the more westerly ranges of this 

 system. In the Coast Mountains of California or Oregon, in the Cascade Mountains, 

 01" in the Sierra Nevada, though I have examined outcrops of granite in many thousand 

 different localities, 1 have never seen even a hand specimen similar in character to the 

 red granite of the Rocky Mountains. It will he seen, by reference to the description 

 formerly given of the country bordering the Lower Colorado, that the granites of all 

 the mountain ranges which cross that stream in the lower 500 miles of its course are 

 like those of the Pacific coast, white or grey, and contain a large quantity of alhite. 

 In the bottom of the canon of the ( uvat ( Colorado, north of the San Francisco Mount- 

 ain, where the river Hows in a granitic trough, this rock, which is covered by several 

 thousand feet of Paleozoic strata, is generally grey and fine-grained. It is, however, 

 in many places penetrated by veins, or replaced l>v masses of a bright-red granite 

 very similar to that of the Santa Fe Mountains. This was the first locality in which, 

 Coming eastward from the Pacific, I met with a rock of this character. In the Alle- 

 ghanies, or the mountains of New England, I have never seen any granite like that 

 of the Rocky Mountains, hut. in the bowlder-drift of the Mississippi, and in places 

 north of the great lakes, a rock is found much more closely resembling it. In this, 

 however, the crystals of feldspar are of a less decided red than those of the Canadian 



rock, being pale rose-red, those of Santa F6 a bright brick-red. To the erosion of the 

 red granites of the Pocky Mountains, during the Paleozoicand Secondary ages, I have 

 keen inclined to attribute the prevailing red color of so large a part of the sedimentary 

 recks. On the hanks of the Colorado, several hundred feet of the Carboniferous strata 

 consist of blood-red sandstones and shales, with large quantities of gypsum ; nearly the 

 entire interval between the summit of the Carboniferous system and the base of the 



( Jretaceous is filled with similar materials, and some portions of the Ppper ( Yetaceoiis 

 strata have the same decided tint. 



The granite of the Santa Fe Mountains is not universally of the character I have 

 described; occasionally it is seen to he light-colored, grey or white, as it is near Pock 

 Corral, a few miles east of Santa Fe, on the Independence road. Veins of quartz 

 and epidote arc; very common in the granite of the Santa Fe Mountains; the former 

 being numerous and large. I was never able, however, to discover in them any traces 

 of metallic minerals. They are certainly not the repositories of the copper, lead, 

 silver, and gold which an; found in the region immediately about Santa Fe. 



