4oG PROCEEDINGS OF THE ACADEMY OF [1890. 



iu Hipi)uritic remains, which crops out at Apasco, and which has 

 been referred to by Ramirez iu his " jNIemoria para la Carta Geol- 

 ogica del Distrito de Zumpango."^ I have seeu the fossils from this 

 region, and am satisfied that they are largely identical with those 

 found in the Hippuritic limestones on the south side of the Mexican 

 plateau, in the mountains of Tehuacan and of Yautepec. Virlet 

 d'Aoust mentions the occurrence of broadly-distributed beds con- 

 taining Ananchytes sulcata, but it has not been my good fortune to 

 meet with this very characteristic fossil of the Chalk (Senonian), 

 nor have I seen it in any of the collections of Mexican fossils. 



Without doubt the limestone of Tula and Apasco is identical with 

 that which Biircena has recorded as occurring in Queretaro, and in 

 the districts of Yolotepec, Zimapan and Jacala, iu the State of 

 Hidalgo, where the rock contains impressions of Hippurites, Radio- 

 lites and Nerinseas.^ That this is a part of the true typical Upper 

 Cretaceous formation, the character of the fossil remains, it appears to 

 me, abundantly proves. Biircena, while recognizing the Cretaceous 

 age of the formation, mentions the occurrence in it of a supposed Ju- 

 rassic fossil, Nerimea hieroglyphica. The same fossil was also found 

 by Barcena, associated with Hippurites, Radiolites (referred to as 

 Crania), etc., in the rock of the Cave of Cacahuamilpa, in the north- 

 ern part of the State of Guerero, and the distinguished Mexican 

 geologist was originally led to conclude from this occurrence that 



Cretaceous Beds of the Eastern and Southern United States;" "The Neozoic 

 Geology of Southwestern Arkansas," Report Geol. Siirv. Arkansas, 1888, p, 106). 

 The statement is, however, erroneous : Exogyra coslata is an abundant fossil of 

 the red sands which underlie or form the base of the Middle Marl Bed (as may 

 be seen in the section at Mullica Hill), where it is associated with Gryphea vesicu- 

 laris, Belemnitella mucronata, etc. Its position, in fact, is very near to the top of 

 the Cretaceous series of the State. 



It is much to be regretted that American geologists so persistently use the al- 

 most meaningless terms " upper" and "lower" as applied to formations occurring 

 in special localities, without determining or stating the relations of such terms in a 

 general geological classification. This indiscriminate use of broad subdivisions 

 cannot but lead to confusion. How often we hear mention of Lower, Middle and 

 Upper Cretaceous deposits of New Jersey, when in reality beds referable only to 

 the Senonian and Daman (possibly also the Turonian) — consequently, equivalents 

 only of the higher Cretaceous of the continent of Europe and of England — are in- 

 tended; indeed, a Jurassic deposit has even cropped up in the same StatC) 



1 Anales del Ministeriode Fomento, Mexico. 



2 Anales del Ministerio de Fomento, Mexico, 1, 1877, p. 349. 



