50 EXPLORING EXPEDITION FROM SANTA FE 



CRETACEOUS FORMATION. 



* 



Kxcept for the surface erosion, which has so greatly modified the topography of 

 the region surrounding Santa Ft', we should still find the Cretaceous strata reaching 

 high up on the slo|>es of the mountains and completely covering the underlying rocks, 

 now so freely exposed, both on the mountain-sides and in the valleys of the streams. 

 So deej) and wide-spread has been the denudation, however, that, from the mountains 

 proper, the Triassic and Cretaceous rocks have been wholly removed, and of the 

 sedimentary series nothing- but a part of the Carboniferous strata is left. The Triassic 

 beds are generally soft and have offered little resistance to the mountain-torrents which 

 have acted upon them, but they were once all covered with the massive, though not 

 hard, sandstones of the Lower ( Cretaceous group, and, wliere these were not broken up 

 by the upheaval of the mountain crests and cones, they have protected the lied Beds 

 below, so that we find the latter in full thickness all around the bases of the mountain 

 masses, still covered by the harder strata to which they owe their preservation. 



The Upper Cretaceous rocks are also soft, and it is now necessary to go a long 1 

 way from Santa Fe before anything like a fair representation of the upper portion of 

 this series can be found. Indeed, east of the mountains the extreme Upper Cretaceous 

 strata are only seen in place near the Mississippi and the Gulf of Mexico. In tlie 

 valley of the Rio Grande none remain, and it is only after crossing- the main divide, 

 between the waters of the Atlantic and Pacific, and seeing the magnificent exposures 

 of the Cretaceous series in the valley of the Sail .Juan, that we can form a just con- 

 ception of the grand scale on which the Chalk formation was originally built up in 

 New Mexico, or of the enormous denudation which this region has suffered since it 

 was raised above the surface of the ocean. The attention of every traveler over the 

 great central plateau of our continent is attracted to the canons which give character 

 to the scenery, and when he learns that they are simply the effects of surface 

 erosion, they become sources of unending wonder and interest; but, notwithstanding 

 their magnitude and impressiveness as records of the lapse of countless ages, it is quite 

 certain that they are referable to a single producing cause, viz., the slow, though con- 

 stant, erosive action of running water. The proof of the truth of this assertion is given 

 in my report on the geology of the country bordering the Lower Colorado, to which 

 I have already frequently referred. 



In the description of the Cretaceous strata, which came under our observation on 

 our first expedition through New Mexico, I divided them into two groups, which I 

 denominated Upper and Lower Cretaceous ; that being the most simple and natural 

 division of the strata exposed in Kastern New Mexico and the Indian Territory. I had 

 at that time, however, no opportunity <>f examining the extreme upper portion of the 

 formation, and it was only when, going west from Santa 1'V, we had passed the divide 

 between the waters of the Atlantic and Pacific, that we gained any knowledge of the 

 upper thousand feet of the series. These we found to be made up of a group of rocks 

 quite unlike, in lithological characters and fossils, the calcareous beds Upper Creta- 

 ceous of my former report of the banks of the Canadian. These true Upper Creta- 

 ceous beds will be described in detail in a. subsequent chapter, and, as they do not 



