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



American Cretaceous beds so harmoniously developed in 

 northern Mexico and in the Texas region. The first of these 

 papers is the excellent monograph by Drs. Felix and Lenk, 

 and summarizes the occurrence of the Cretaceous formation 

 in Mexico as follows :* " The Cretaceous formation in Mexico 

 is divided into two parts. 1. The Upper part (the ' Hip- 

 purite ' limestone) is characterized by many Hippurites and 

 Padiolite-like forms and numerous ISIerineas. This is princi- 

 pally thick light gray sometimes flinty limestone. 2. Below 

 this (they note no break) are light blue-gray sometimes black 

 limestones with local intercalations of marly layers," which we 

 shall hereafter allude to as the Monoplenra beds of Tehuacan. 

 The uppermost of these formations or 'Hippurites' limestone 

 they do not describe at length, but passingly refer it to the 

 Upper Cretaceous. The lower or Monopleura beds of Tehua- 

 can, they refer to the Neocomian. 



The second paper is by Prof. Angelo Heilprinf of Phila- 

 delphia, who, without giving any distinct subdivision or strati- 

 graphic details recognizes only the Hippurites limestone and 

 opposes the careful determination of the JNeocomian by Felix 

 and Lenk by saying : " No unequivocal deposits of Lower 

 Cretaceous age — as equivalent of the Gault, Neocomfan, etc., 

 have yet been discovered in the Republic ; the Mexico deposits 

 represent a horizon not lower than the Cenomanian while the 

 great bulk of the formation is of Turonian and Cenomanian 

 age.";}; 



The diverse conclusions of these two papers can be explained, 

 as I ascertained in Mexico, upon the ground that neither saw 

 the regions of the full occurrence of the Cretaceous formations 

 of Mexico or the sequence and relations of their divisions. 



At most they describe only two of the many horizons in the 

 great sequence of the Lower Cretaceous beds while the equally 

 important but distinct Upper Cretaceous formation or Meek 

 and Hayden series entirely escaped their observation. 



* Beitrage zur Geologie unci Paleontologie der Republik Mexico, von Dr. J. 

 Felix unci Dr. H. Lenk: in two parts, Part I, Leipzig, 1890 ; Part III, Stuttgart, 

 1891 (Part II not published). 



\ The Geology and Paleontology of the Cretaceous Deposits of Mexico, by 

 Prof. Angelo Heilprin, Proc. Philadelphia Academy of Natural Sciences, 1890, 

 pp. 445-469. 



\ Prof. Heilprin also concludes that " No true Lower Cretaceous deposits exist 

 or have so far been identified in either Arkansas or Texas, the Lower Cretaceous, 

 so-called (Comanche Series, etc.) being not older than the Cenomanian (Middle or 

 Upper Cretaceous)." I cannot here discuss this conclusion of Prof. Heilprin's 

 concerning a region he had not seen and with whose unpublished paleontology 

 his writings show unfamiliarity. While the upper part of the Comanche Series is 

 undoubtedly of Middle Cretaceous affinities he seems unacquainted with the exist- 

 ence of the Lower Trinity division with its G-len Rose fauna of Neocomian mol- 

 lusks and Potomac, or Wealden, plants. 



