42 EXPLORING- EXPEDITION FROM SANTA FE 



Of the two great mountain chains visible from Santa FC", referred to in the pre- 

 ceding pages, the Sandia and the Valles, the former is so fully described in the reports 

 of other geologists (Messrs. Marcou and Blake), and in my report upon the geology of 

 the country bordering the Colorado, that it is scarcely necessary that anything more 

 should now be said in reference to it. The Valles, lying west of the Rio Grande, will 

 be more appropriately noticed hereafter in the description to be given of the geology 

 of the country between the Rio Grande and the Colorado along the route of our ex- 

 pedition. This region includes numerous important mountain ranges, which will be 

 best examined from a point of view where their relations can be most clearly seen. 



The stratified rocks of the neighborhood of Santa Fe now claim our attention, and 

 the features which they present will perhaps be most readily appreciated from a resume 

 of each formation considered by itself. 



CARBONIFEROUS STRATA. 



The rocks of this age are exposed in numerous localities in the vicinity of Santa 

 F6", and are apparently the oldest sedimentary strata represented in that region. It is 

 possible that Devonian and Silurian rocks exist in this part of New Mexico ; but if so, 

 they have hitherto escaped detection, and are probably concealed by a covering of 

 more recent materials. It is certain that at Santa F6, in several localities where I had 

 an opportunity of seeing the line of junction of the sedimentary and crystalline rocks, 

 the Carboniferous limestones, the equivalents of the Coal-Measures, rest directly upon 

 the granite, or a layer of coarse sandstone two or three feet thick intervenes, the only 

 possible representative of the older rocks. It will be remembered by those who have 

 read the description given in the report of Lieutenant Ives of the section presented 

 in the canon of the Great Colorado, that in the table-lands west of the Rocky Mount- 

 ains an interval of over three thousand feet occurs between the base of the Coal- 

 Measure limestones and the surface of the granite. This interval is filled by a series 

 of limestones," shales, and sandstones, which I have supposed to represent the Lower 

 Carboniferous, Devonian, and Silurian formations. All that great mass of sediment is 

 wanting at Santa Fe. It is wanting, too, on the more westerly ranges of the Rocky 

 Mountains, and also from those which border the table-lands at their western verge. 

 The absence of this group of rocks in all these localities seems to me to be accounted 

 for only by supposing that they were deposited after some of the great lines of up- 

 heaval which traverse the central portion of the continent had already attained consid- 

 erable elevation above the surfaces which bordered them. The facts revealed in the 

 canon of the Colorado show plainly that the granitic basis of this country was consol- 

 idated previous to the deposition of the Paleozoic strata, and that over many of the 

 minor irregularities of the sea-bottom the older sedimentary rocks were quietly and 

 horizontally laid down, surrounding and abutting against granitic pinnacles, which 

 rose above the shallow waters in which they were deposited. These inferences, if con- 

 firmed by future observations, will considerably modify the hitherto accepted ideas in 

 regard to the age of the ranges of the Rocky Mountains. We are at least warranted 

 in the conclusion that these great lines of fracture in the earth's crust are few of them 

 wholly of modern date, and it even seems probable that through all the geological 



