AMMONITES BARNSTONI. 



311 



ber of the Cretaceous formations in Western Iowa and the 

 adjoining territories of Nebraska and Kansas, and its 

 extension below the line where any well-marked Creta- 

 ceous species have been found, " suggests very strongly 

 that we shall yet find lower geological formations, or 

 those of the age of the Jura, or Oolite of Europe."* 



The discovery of Oolitic or Liassic rocks in Exmouth 

 Island by Captain Belcher ; of Ammonites, Spirifer, Pec- 

 ten, &c. by Captain McClintock in Prince Patrick Island, 

 lat. 76° 30', long. 117° W. in localities corresponding to 

 the northerly trend of the Carboniferous limestone of the 

 Eocky Mountain region, and the great thickness of the 

 rocks on an outlier of the Liana Estacado below any well 

 marked Cretaceous fossils, indicate, Mr. Hall thinks, " the 

 probable occurrence of lower fossiliferous rocks, or those 

 of Jurassic age, along the whole length of the Eocky 

 Mountains, and probably coextensive with the lower 

 members of the Cretaceous Series." 



Ammonites Barnstoni. (N. S.) 



[Shell compressed, subglobose, broadly rounded on the 

 dorsum, and prominent or subangular around the um- 

 bilicus which is deep, conical, and nearly as broad as the 

 outer whorl. Volutions having their greater diameter at 

 right angles to that of the shell ; each of the inner ones 

 about three-fourths hidden in the profound ventral groove 

 of the succeeding turn. Surface ornamented by distinct 

 regular costas, which are sharply elevated around the um- 

 bilicus, into small elongated subnodose prominences ; and 

 at less than half the distance across the sides of the whorl, 

 their number is increased nearly threefold by division and 



* Geological Survey of Iowa ; page 144. 



