124 Keyes — Dakotan Series of Northern New Mexico. 



Art. XII. — The Dakotan Series of Northern New Mexico ; 

 by Charles R. Keyes. 



Strata that have been referred to the Dakota division of 

 the Cretaceous age have been long known in the Southwest, 

 around the southern end of the Rocky Mountains in northern 

 New Mexico. The section there exposed has been generally 

 regarded as exactly representing the " Dakota Group" as first 

 defined by Meek and Hayden* for the upper Missouri region. 

 Late observations in the New Mexican region indicate clearly 

 that the formation called the Dakota sandstone has never been 

 carefully delimited, that it has been given quite different 

 limits by different authors, and that the section usually so called 

 actually belongs to several geological ages. 



As recently made out, the general Mesozoic section of north- 

 eastern New Mexico presents the following elements : 



General Mesozoic Section of Northeastern New Mexico. 



Age. Series. Thickness. 



f Late 7. Laramian sandstones 2500 



•3 ! 6. Montanan shales 1600 



5 \ Mid 5. Coloradan shales 1000 



*? J 4. Dakotan sandstones 500 



^ Early 3. Comanchan shales 100 



Jurassic 2. Morrisonian sandstones 250 



Triassic 1. Red Beds (upper part) _ 1000 



As usually considered in the literature of the subject, the 

 Dakota sandstone has been made to cover of the above section 

 not only No. 4, but No. 2 and No. 3, and not infrequently part of 

 No. 1. The reasons for these long standing errors of interpre- 

 tation recalls one of the unpleasant chapters in the history of 

 American geology. It goes back to the very beginning, to 

 the early sixties, when there was a concerted attempt to thor- 

 oughly discredit the work of Jules Marcou in this country. 

 The proofs of the conclusions which the Swiss geologist sub- 

 mitted may have been insufficient at the time, or they may 

 have been happy guesses, but the fact yet remains that the 

 latest work in the region has, in the main, substantiated his 

 observations and there are too many of his statements that are 

 correct to assert at this day that they w r ere anything less than 

 a display of geological acumen such as none of his critics pos- 

 sessed. Newberry, Iiayden, Meek and others appear to have 

 become so absorbed in their side of the controversy that they 

 all but lost sight, of the facts, and they not infrequently went 



*Proc. Acad. Nat. Sci., Phila., vol. xiii, pp. 410-420, 1862. 



