THE MORRISON FORMATION 663 



of it, there are gypsiferous shales and gypsum varying greatly in 

 thickness in different exposures, the maximum observed being 

 125 feet. 



Immediately underlying the gypsum and forming the lowest 

 exposures of the region are the Red Beds of which 200 or 300 feet 

 are exposed over a considerable area, where the overlying formations 

 have been removed from a broad, domelike uplift. They consist 

 mainly of coarse, dark-red sandstones with some red and purplish 

 shales and a few thin bands of white calcareous sandstone, which 

 are conspicuous where they form the surface of low mesas. In the 

 upper layers of the Red Beds, below the mouth of Chaquaqua Creek, 

 Mr. Darton has collected a bone that has been identified as Belodon, 

 indicating Triassic age. 



The Purgatoire section may be summarized as follows: 



1. Benton shales, thickness probably not more than . . . 200 feet 



2. Dakota sandstone 100 " 



3. Dark shales and shaly sandstones with Comanche fauna . 50 to 100 " 



4. Coarse gray, cross-bedded sandstone 15 to 60 " 



5. Variegated shales, marls, sandstones and limestones of the 



Morrison formation, with Brontosaurus, etc 200 " 



6. Gypsum and gypsiferous shales 70 to 125 " 



7. Red Beds with Belodon near top, exposed 200 to 300 " 



With some variations in thickness and, in a few cases, the disap- 

 pearance of one or more members, this section is essentially repeated 

 throughout the area we examined in Oklahoma and New Mexico 

 as far south as Tucumcari. 



Two Buttes uplift.— On the way south from Lamar, Colorado, to 

 the Cimarron in Oklahoma, the exposures were examined near Two 

 Buttes, where Mr. Darton 1 had found the Comanche Gryphaea 

 corrugata. Here the so-called Lower Dakota, beneath the fossil- 

 iferous Comanche shales and sandstones, appears to rest directly on 

 the eroded surface of the Red Beds. Several additional Comanche 

 species were collected, including P achy discus brazoensis (Shumard), 

 and incidentally it was determined that the oyster bed reported by 

 Darton as occurring in the Dakota of this region is probably beneath 

 the true Dakota and in the Comanche. 



1 Science, New Series Vol. XXII, July 28, 1905, p. 120. 



