360 Keyes — Unconformity in Central New Mexico. 



Art. XXXYTII. — Unconformity of the Cretaceous on Older 

 Rocks in Central New Mexico ; by Charles R. Keyes. 



In New Mexico Cretaceous sedimentation is enormously 

 developed. The total thickness of the strata referable to this 

 age cannot be less than 7000 feet. 



In eastern New Mexico and Texas the sequence of the Cre- 

 taceous formations is quite complete. Both the Lower Creta- 

 ceous and the Upper Cretaceous are well represented. Below 

 are the "Red Beds," probably composed partly of Triassic 

 sandstones and shales and partly of Carboniferous layers of 

 similar lithologic characters. These attain a thickness of 2000 

 feet and upwards. Then below all these are the great Carbon- 

 iferous limestones, which are about 2000 feet thick and which 

 form the backslopes of most of the block mountains of the 

 Basin region. The generalized geological section for New 

 Mexico may be tabulated as follows : 



Ages. 



Systems. 



Thickness. 



Formations. 



Eocks. 



Cenozoic 



Quaternary 

 Tertiary 



200 





Gravels 





200 

 800 



Galisteo 

 Puerco 



Sandstones 

 Clays 



Mesozoic 



Cretaceous 



2000 



J500 



800 



400 



800 



Laramie 

 Montana 

 Colorado 

 Dakota 

 < Comanche 



Sandstones 

 Shales 

 Shales 

 Sandstones 





Sandstones 





Triassic 



1000 



Cimarron 



Shales 



Paleozoic 



Carboniferous 



1000 

 300 

 300 

 200 



Bernalillo 

 Madera 

 Sandia 

 Lake Valley 

 Chloride 

 Pinos Altos 



Shales 

 Limestones 

 Limestones 

 Limestones 





Devonian 

 Ordovician 



200 



Limestones 





400 



Limestones 





Cambrian 



300 



Tonto 



Sandstones 



Azoic 



Algonkian 



300 



1000 



500 



Chuar 

 Grand Canyon 

 Vishnu 



Shales 



Sandstones 



Quartzites 





Archean 



2000 





Schists 



The relationships of the Cretaceous system to the other 

 formations, as displayed in central New Mexico, have long 

 been a puzzle. Throughout the region the Red Beds consti- 

 tute a conspicuous and important formation. Owing, how- 



