H. T. Hill — Cretaceous Formations of Mexico. 315 



Choffat* they will no longer doubt the homotaxial identity of 

 the beds but will be astonished at the wonderful and striking 

 generic identity. The fossil beds of the Washita division or 

 upper part of the Comanche Series from which Prof. Heilprin 

 draws his conclusion that there is no Lower Cretaceous in 

 America are Gault, and not Cenomanian as he alleges, although 

 Marcou referred them to the Neocomian.f Until the writer's 

 paleontological data can be published in full it will be difficult 

 to eradicate the existing erroneous impressions concerning the 

 North American Cretaceous but he strongly maintains that we 

 have in this country in the Atlantic sedimentation of both 

 Cretaceous Series a complete representation of the principal 

 divisions of the Cretaceous period in Europe, presenting a 

 remarkable homotaxial resemblance in many of their subdi- 

 visions, and which, instead of upsetting the canons of paleonto- 

 logic and stratigraphic laws, as has been maintained, verifies 

 the great principle that sedimentation and life on both sides 

 the Atlantic basin presented in Cretaceous times the same 

 generic resemblances and specific variations that it has in all 

 time and that it does to-day, and that the American Cretaceous 

 formations laid down in the open Atlantic waters present far 

 more intimate resemblances to those of similar deposition in 

 Europe than they do to those of the Pacific border only a few 

 miles distant. 



It is evident that the Lower Cretaceous or Comanche Series 

 in Mexico verifies some of the principles already announced 

 concerning it in our own country, to wit : that the deposits 

 there are the deeper water sediments of an oceanic border 

 which had its littoral across the southern end of our own repub- 

 lic, and that they record the progressive encroachment from the 

 southward of the sea upon the Pre-Cretaceous (Jurassic) North 

 American land accompanied by subsidence of the latter. As 

 shown by the rapid shallowing of the sediments in the Washita 

 sub-epoch at the close of Comanche time the profound Lower 

 Cretaceous subsidence reached its culmination during the 

 Fredericksburg sub-epoch and the northern littoral ferruginous 

 beds of the Washita division probably marked the northern 

 border of this Lower Cretaceous or Comanche ocean. This 

 rapid elevation at the close of the Comanche also explains the 

 disappearance of the aberrant Chamidse and Rudistse from 

 sediments of later age in the Comanche series than the 

 Caprina limestone, while some of the forms continue to the 

 top of the Gault in Europe. 



* Recueil de ^Tonographies Stratigraphiques sur le Systeme Cretacique du Portu- 

 gal, par Paul Choffat. Lisbon, 1 883. 



