128 Keyes — Dakotan Series of Northern New Mexico. 



solely upon litliological characters and stratigraphy, since testi- 

 mony of fossils is either unattainable or indecisive. When 

 the work shall have been prosecuted in detail and carried sys- 

 tematically toward the south and west to localities already 

 well determined by evidence of fossils, this classification may 

 prove to be somewhat arbitrary. For the present, however, it 

 seems desirable to include under one group the Dakota of 

 Meek and Hay den and the greater part of the Triassic of authors 

 found in New Mexico. The whole series may be Triassic or 

 it may be wholly Cretaceous. It is included under the Dakota 

 here merely for convenience of description." 



It is quite clear from a consideration of the various localities 

 mentioned that the author had somewhat mixed his strati- 

 graphy, a fact not to be wondered at when the limited time 

 he had for examination is taken into account. His " Upper 

 Dakota" of one locality is the "Lower Dakota" of another. 

 Elsewhere the latter is of undoubted Early Cretaceous age, 

 and not Mid Cretaceous (Upper Cretaceous) at all. 



So far as is known, it is largely due to this report that the 

 confusion regarding the delimitation of the Dakotan series 

 arose in this region. Although the Hayden reports make scant 

 reference to the [New Mexican region, the various allusions are 

 of similar tone. And the way was paved by Newberry's 

 denunciations of Marcou based upon very incomplete observa- 

 tions. 



In northwestern New Mexico, Holmes'* ascribes about 

 1,200 feet of strata to the Dakota group, which he divides 

 into "Lower" and "Upper" portions. Only the massive 

 Upper division is now regarded as properly representing the 

 Dakotan series. The so-called " Lower Dakota " formation is 

 quite different lithologically from the "Upper" portion, and 

 Duttonf more recently gave it the name of Zimi sandstones. 

 It is now regarded as Jurassic in age, as already noted. 



In later years Cummins^: has proposed to put the attenuated 

 Dakota sandstone, as exposed in the Cerro Tucumcari in east- 

 ern New Mexico, with the Early Cretaceous and Jurassic 

 formations of that section, and to call the whole the Tucum- 

 cari beds, or formation. 



The unity of the great sandstone plate as a distinct and 

 easily recognizable stratigraphic formation seems to be now 

 fully demonstrated, and also finds corroboration in the recent 

 observations of Stanton in southeastern Colorado. The name 

 Dakotan series is properly restricted to it. 

 State School of Mines, Socorro, New Mexico. 



*U. S. Geol. and Geog. Sur. Terr., 9th Ann. Kept., p. 224, 1877. 

 t U. S. Geol. Sur., 6th Ann Kept., p. 140, 1886. 

 % Texas Geol. Sur.,' Third Ann. Kept., p. 201, 1892. 



