524 R. T. HILL — THE COMANCHE SERIES. 



if not identity, and Mr. Jules Marcou, in liis geology of North America, has 

 shown many of these to be of Neocomian occurrence. There are other spe- 

 cies, however, which are characteristic of the Gault. The upper, or Meek 

 and Hayden, section of the North American Cretaceous shows, in its dicoty- 

 ledonous plants, its ammonitidse, its echiuodermata, its ostrseidse, its ino- 

 cerami, and in its other fossils, a remarkable resemblance to the European 

 upper Cretaceous faunas, i. e., the Ceuomanian and Senoniau. But iu the 

 American upper Cretaceous strata there is an utter absence of Hippurites 

 and Nerinwa, genera which so abundantly occur in Europe. 



This discordance of paleontologic occurrence of species, however contrary 

 to the tenets of ancient descriptive paleontology, is in thorough harmony 

 with modern biologic and stratigraphic doctrines ; for the species would re- 

 quire great intervals of time to migrate the long distance between Texas 

 and Europe, during which intervals wide differences in sedimentation and 

 stratigraphy would occur. 



The writer fully realizes that, notwithstanding the years of labor of his 

 able predecessors and himself, we have as yet only begun the study of this 

 great series, and that there still remains in them an extensive field for patient 

 investigation. 



