50 EXPLORING EXPEDITION FROM SANTA FE 



CRETACEOUS FORMATION. 



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

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

 high up on the slopes of the mountains ami completely covering the underlying rocks, 

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



So deep and wide-spread lias been the denudation, however, that, from the mountains 

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

 sedimentary scries nothing hut a part of the Carboniferous strata is left. The Triassic 

 heds arc generally soft and have offered little resistance to the mountain-torrents which 

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

 hard, sandstones of the Lower ( Yetaceous group, and, where these were not broken up 

 by the upheaval of the mountain crests and cones, they have protected the Red Heds 

 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 I pper Cretaceous rocks are also soft, and it is now necessary to go a long 

 way from Santa F6 before anything like a lair representation of the upper portion of 



this series can be found. Indeed, east of the mountains the extreme I'pper ( Yetaceou s 

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

 valley of the Rio Grrande none remain, and it is only alter 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 San 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 sccnerv, 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 lane 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 Eastern New Mexico and the Indian Territory. I had 

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

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

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

 upper thousand feet of the series. 'These we found to be made up of a groupofrocks 



quite unlike, in lithological characters and fossils, the calcareous beds — I'pper Creta- 

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

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



