446 CHARLES R. KEYES 



To the eastward of the Estancia Plains there are three important 

 "red-beds" formations, each nearly i,ooo feet thick, and superposed 

 upon one another. They are of widely different geologic ages, and 

 are separated by great erosional unconformities. One is of Mid- 

 Carbonic Age, another of Late Carbonic Age, and the third of Triassic 

 Age. Besides these red-beds there have been long recognized in the 

 region other great red-colored terranes, in the Cretacic section, in the 

 Tertiary section, and in the Devonic section. 



At the base of the Cretacic section of this region the Rio Mora 

 sandstone is an important member. It is the so-called Dakota 

 formation of the early geologic reports of the Southwestern United 

 States. 



Unconformities. — All of the serial formations of New Mexico, as 

 well as many of their minor members, are separated by marked planes 

 of unconformity. Some of these indicate only notable oscillations of 

 the old shorelines; but several of them are manifestly ancient erosion 

 surfaces. Of the latter class may be mentioned the intervals repre- 

 sented by the sedimentation discordance between the Huronic crystal- 

 lines and the Manzanan series, between the Cimmaronian and the 

 Maderan, between the former and the Triassic, between the Triassic 

 and the Cretacic, and between the last mentioned and the Cenozoic 

 deposits. 



In the interval between the top of the fundamental complex and 

 the Manzanan limestones, there are missing all of the Cambric, the 

 Ordovicic, the Siluric, the Devonic, and the Early Carbonic sequences. 

 These are all very fully represented in the southern part of New 

 Mexico. The interval between the Maderan series and the Cim- 

 maronian shales and sandstones is occupied, a hundred miles south 

 of the Estancia region, by about 3,500 feet of limestones and sand- 

 stones, known as the Guadalupan series and regarded as representing 

 the true Permian of Russia. The great sequence of "red-beds," so 

 long of uncertain geologic age, has thus lately been found to be partly 

 of Mid-Carbonic, partly of Late Carbonic, and partly of Triassic Age; 

 the three parts being separated by marked unconformities. A marked 

 erosion unconformity also separates the Triassic shales from the Mid- 

 Cretacic sandstones of the so-called Dakotan series. The missing 

 terranes, represented by the Morrison beds of Jurassic Age and the 



