Kt 



Unconformity in Central New Mexico. 361 



ever, to the peculiar position they occupy when well exposed 

 on the lower backslopes of the block mountains, with the Cre- 

 taceous coming in immediately, the exact disposition of the 

 two great formations is seldom clearly discernible. Then, too, 

 at the bases of mountains vast plains stretch away, which are 

 deeply covered by gravels, sands and clays washed down from 

 the higher elevations, and which cover effectually all traces of 

 the indurated rocks beneath. While these underlying rocks 

 usually are more or less highly inclined, they have been com- 

 pletely bevelled off to a surface that is as even and level as 

 the plains themselves. 



That the Cretaceous rocks in central New Mexico rest 

 uneonformably on the older formations has been for some time 

 surmised. The difficulty has been to obtain indisputable evi- 

 dence in support of this hypothesis. This proof has lately 

 been secured ; and the facts are of exceptional interest. 



Sca-Ze 



Fig. 1. Cretaceous and Eed Beds at Tejon, New Mexico. 



In a number of instances the Cretaceous sandstones have 

 been found to repose apparently in perfect conformity upon 

 the Carboniferous limestones. There is no evidence whatever 

 of the existence of the great thickness of Red Beds between 

 sandstone and limestone. If the Red Beds ever existed there 

 they were swept cleanly away from the surface of the lime- 

 rock. But the bedding planes of the Carboniferous and Cre- 

 taceous formations were to all appearances parallel. 



East of the Sandia Mountains the Cretaceous deposits extend 

 almost uninterruptedly to the Texas line. At the north end 

 of the range where the backslope of Carboniferous limestone 

 begins to sink under the plains, a small stream has cut deeply 

 through the Cretaceous sandstones into the Red Beds beneath. 

 At this place the Red Beds are standing on end, while the yel- 

 low Cretaceous beds are lying very nearly horizontally. The 

 relationships are best indicated by diagram (figure 1). 



