C. B. Keyes — Triassic System in. JVew Mexico. 423 



Art. XLIII. — -Triassic System in New Mexico ; by Charles 



R. Keyes. 



The " Red Beds " of the Southwest, from central Kansas to 

 the Grand Canyon, have long defied every attempt to deter- 

 'mine their geological age, and to satisfactorily settle even the 

 larger problems connected with their stratigraphy. In Kansas, 

 in Oklahoma, in Texas, and on through New Mexico and 

 Arizona to Utah, these formations have for more than half a 

 century remained a puzzle. Those who have had to give some 

 attention to the Red Beds have, in the absence of abundant 

 characteristic fossils, considered the entire sequence either Tri- 

 assic in age or (so-called Permian) Carboniferous. 



Since the making of extensive examinations of the Red Beds 

 formations over broad areas in New Mexico and the adjoining 

 states during the past few years, it has been found that there 

 are a number of important general features that have either 

 not received the attention they deserve, or have escaped notice 

 altogether. When two years ago I made the statement* con- 

 cerning the Kansas section, that after seeing at close range the 

 Red Beds of New Mexico sufficient data had been obtained to 

 clearly demonstrate that their stratigraphy could not be unrav- 

 eled on the basis of the Kansas scheme, the separation of 

 the Red Beds into their component parts was then beginning 

 to resolve itself into a satisfactory reality. 



The Red Beds do not form the homogeneous succession that 

 they have been generally regarded as doing. Lithologically 

 they are broadly divisible into two easily distinguishable 

 parts. There is a large portion of the- entire section composed 

 of heavy argillaceous shales and clayey sandstones usually of 

 deep red colors, rather uniform throughout, with much gyp- 

 sum intercalated and disseminated, and with saline shales 

 abounding. The upper part consists of light, sandy shales 

 chiefly, with some heavy sandstones; the colors, while prevail- 

 ingly reds, are quite varied; gypsum and saline shales are pres- 

 ent only sparingly. The plane separating the two parts of the 

 Red Beds section, as thus defined, is, when once recognized, 

 a conspicuous one. 



In eastern New Mexico, in the Canadian and Pecos valleys, 

 around the northern and western margins of the Llano Esta- 

 cado, there is at the base of the upper one of the two terranes 

 a well marked conglomerate that has been widely traced. Un- 

 conformable relationships exist between this and the strata 

 beneath. In western Texas, Drakef and Cummins have also 

 well established these facts. 



* American Geologist, vol. xxxii. pp. 218-223, 1903. 

 f Texas Geol. Sur. , Third Ann. Kept., p. 227, 1892. 



