386 Marcou’s Geological Map of the United States. 
much broader coloring representing the trias. Yet there is no 
sufficient evidence of the presence of Jurassic formations, and 
the Llano and other plateaux referred to that age are not Jurassic, 
one of the mounds separated from the Llano Estacado by ero- 
sion. The Gryphwa is said to have the greatest analogy with 
ear much resemblance to O. Marshii of the inferior Oolite of 
Europe.* In the text accompanying the map the species are 
announced as identical, one with’ @. dilatata, the other with 0. 
Marshii, Even if this identity be admitted, it does not author- 
ize the conclusion that the strata are beyond question Jurassic; 
or if it did, the occurrence of Jurassic at that one point on the 
Canadian, would not authorize us to conclude that the formation 
extends for more than a thousand miles on both sides of the 
mountains. The genus Gryphea in America is eminently char- 
acteristic of the Cretaceous formation, and species which very 
closely resemble G. Tucumcari, if not in fact identical with it, are 
very abundant in Alabama and New Jersey in the Cretaceous 
formation. Moreover, all the species are found with many varia 
tions according to the locality. The abundance and variety of 
the species of this genus render it unsafe to regard (@. Zucwm- 
sea are found in the government collection, but there are 
none of the Ostrea, 
across 
the mountain chain, through the passes, into the valley of the 
Rio Grande, and here near the summit of the table-lands just 
il umerous 
specimens of Inoceramus have also been obtained by Simpson,+ 
* See Resumé of a Geological reconnoissance, &c. R f Lieut. A. W. Whip- 
ple, U. S. Top. Engrs., H. Doe. 129, chap. vi. p aaierg nie at 
+ Described and figured by Prof. Bailey—Report by Lieut. J. W. Abert, U. 5: 
oT Engrs. > Srghmaer yom of New Mexico. by 
; ar ; p of the Route from Fort Smith, Arkansas, to Santa Fé, 
Lieut. J. H. Simpson, U. 8. Top. Engrs, Washington, 1850. : 
