93 



Upper Cretaceous 

 or 

 Stoonien. 



Austin Limestone. 



Fi?h-bed in sandstone (L.' Arenaceous group with 

 Ttxana). | Oitrea congesta. 



Blue Marl with Inoceramus Fish-bed, Lamna Ttxana, 

 problematictis. \ gjg_ 



Middle Cretaceous 



or 

 Green Sand and Turonian, 



Marly clay, or Eed River group. 



Caprlna limestone. 



Comanche Peak group (superior part with Exogyra 

 Texana). 



Exogyra arietina Marl. 



Lower Cretaceous 



or 

 Aptien and X^ocomien. 



Washita limestone (comprising the inferior part of the 

 Comanche Peak group, with Gryphaa Pitcheri). 



Caprotina limestone. 



Trias or Carboniferous. 



Dr. Benjamin Sbumard in tbis memoir not only synchronizes all 

 the strata of my real section of Pyramid Mount, near the Llano 

 Estacado, with his theoretical section of Texas, and that with such a 

 degree of certainty that he thinks it " scarcely admits of a doubt," 

 but he also regards my Grypli(Ea Tucumcarii as identical with his 

 Gri/phoea Pitcheri^ and my Ostrea Marsliii with his 0. subovata of Fort 

 Washita. I have the greatest respect for the labors of Dr. B. Sbu- 

 mard, who is one of the pioneers of the geology of the Mississippi 

 valley, and I do not doubt that he candidly believes he has given a 

 right interpretation to my observations at Pyramid INlount. But 

 however great may be the weight due to the opinion of such an 

 eminent observer, especially when it concurs with that of all other 

 explorers, collectors, and Messrs. Meek, Hall, and Newberry, I con- 

 tinue to believe, very candidly also, that there is not a single stratum 

 nor a single fossil of Cretaceous age at Pyramid Mount. Dr. Shu- 

 mard thinks that a closer observation than mine at Pyramid Mount, 

 would result in the discovery of the cretaceous fossils of Grayson 

 County, and that my Ostrea Marsliii and G. Tucumcarii, identical or 

 not with his 0. subovata and G. Pitcheri, " hold a position more than 

 two hundred feet above strata that contain well-marked cretaceous 

 types." I can only express the wish that when Dr. Shumard goes to 

 Pyramid Blount, he may find more fossils than I did, and if any of 

 them are cretaceous, and beloiu the Gnjphoea Tucinncarii bed, I am 

 ready to yield to such a proof. 



The Gryplixa Tucumcarii is a Jurassic fossil closely allied to G. 



