GEOLOGICAL SETTING OF NEW MEXICO 249 



As the uppermost member of the Cretaceous section the 

 Laramian series embraces only a small part of the beds formerly 

 paraded under this title. By divesting the old Laramie section of 

 that portion which is really Tertiary in age the long drawn-out 

 controversy concerning the true age of these beds comes to an 

 abrupt end. 



With the principal coal beds referred to the Montanan series 

 below and the Ratonan series above the so-called Laramie formation 

 of New Mexico becomes almost as barren as the marine Coloradan 

 series. Still, in the northwestern part of the state, the Pictured 

 Chffs sanstones and the Navajo shales attain a thickness of nearly 

 1,200 feet. 



Tertiary sedimentation in the New Mexican area begins with 

 beds the deposition of which seem long to antedate the earliest 

 Eocene formations of other parts of the world. When in the 

 course of coal investigations in 1906 a marked erosional uncon- 

 formity and basal conglomerate were found in the lofty Raton 

 Mesa about 1,500 feet below its massive lava cap, it was surmised 

 that the solution of the Laramie problem had been stumbled upon 

 and that above the erosion plane the beds were really Tertiary in 

 age, while those beneath that line were Cretaceous. These con- 

 clusions were fully substantiated a decade later by Lee in an 

 elaborate monograph on the geology of the region. 



The Ratonan series is, then, older than the oldest Eocene 

 deposits of the state, the Puerco beds, which, since the days of 

 Cope in the region, were believed to be the earliest Tertiaries 

 extant. It is an important coal-bearing section, which fact prob- 

 ably largely accounts for its early confusion with the original 

 Laramie coal formations of the more northern Rocky Mountains 

 districts. The erosion plane upon which the Ratonan sediments 

 rest is a peneplain of wide proportions evidently worn down on the 

 entire southern Rocky Mountains province. In its production no 

 less than a mile of rock was removed. 



The Aztecan series is represented by a basal conglomerate of 

 very considerable thickness. Beyond the borders of the state the 

 Arculeta conglomerate is succeeded by shales. No sediments are 

 correlated with the erosional interval below. It is possible that 



