330 Marcou’s Geology of North America. 
vicinity. The identification in the case of these beds rests upon 
organic remains, as it ought; yet there is the same faith in 
mineral coincidences that has before been pointed out. T 
species mentioned are the Gryphea dilatata var. Tucumcarii, an 
Ostrea very near Ostrea Marshii, a Trigonia and a species of 
Astarte; but the identification rests mainly upon the Ostrea and 
Gryphea, which are figured on plate 4. Great importance, there- 
fore, attaches to the right determination of these species; for if not 
Jurassic, if associated in other strata in the west with well known 
Cretaceous species, they serve as credentials for the Cretaceous 
instead of the Jurassic. 
The bearing of the evidence from these fossils has been dis- 
‘Washita, along with Ammonites vespertinus Morton, ryphed 
phea, were found extensivel 
_ ‘West of the Mississippi by 
J 
n the great west is published as such by Mr. 
dig ows. 
ODE ate eee 
