644 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



F-G 13-14. MEXICO. 



The Upper or Neo-Cretaceous of Mexico is described in general terms by Agui- 

 lera,^" as follows : 



The Neo-Cretaceous is encountered principally in the northern part of the Republic and 

 commences with shales of the lower Turonian characterized by Inoceramus Idbiatus of the 

 Ligerian substage. This substage occurs at Cerro Prieto, at the foot of Cerro Muleros, near 

 the city of Juarez. It is also known in the north of Zacatecas, at Mazapil; in CoahuUa, at 

 Parras and Peyotes, and in the latter locality it contains, besides Inoceramus Idbiatus Schlot- 

 heim, PtychodMS mortoni Mantell, Ptychodus of. wJiiplei Marcou, Ceratodus sp., Tryonix sp., 

 and many teeth of fishes, etc. 



The upper Turonian or the Angoumian and the Emscherian or lower Senonian have not 

 as yet been found in Mexico characterized by their fossils. The rocks of this age in general 

 are shales interbedded with occasional layers of limestone and are unfossUiferous. * * * 



The Aturian h well represented at Cardenas and at Santa Catarina, in the State of San 

 Luis Potosi, betvreen the capital and Tampico, by a fauna very rich in lamellibranchs : Gryphsea 

 vesicularis Lamarck, CoralliocJiama G. Boehmi Bose, Biradiolites cardenasensis Bose, Radiolites 

 austinensis Roemer, Exogyra costata Say; and containing also gastropods — different species 

 of Cerithium, TurriteUa, ActseoneUa, Nerinea; one finds also Orbitoides and a large number of 

 corals. An ActseoneUa fauna is found, likewise in the environs of Monterey, in Nuevo Leon, 

 but on approaching Coahuila ActaeoneUa disappears and Exogyra costata Say, Exogyra ponderosa 

 Roemer, Ostrea glabra var. wyomingensis Meek and Hayden are predominant. The Senonian 

 is found at Las Esperanzas, in Coahuila, where it is formed of calcareous and marly sandstones 

 which alternate with shales, and is terminated in the upper part by glauconitic sandstones 

 characterized by Sphenodiscus lenticularis, lamellibranchs, and gastropods. * * * in the 

 south of Mexico the Senonian has not yet been encountered, and it is probable that erosion 

 has destroyed it in certain places where it may have occurred. 



Sapper described Upper Cretaceous strata of the Province -of Chiapas, but they 

 have been assigned to the " Meso-Cretaceous " (Comanche) by Bose. (See Chapter 

 XIV, p. 589.) 



Regarding the Upper Cretaceous of Mazapil, see quotation from Burckhardt in 

 Chapter XIII (p. 554). 



Local descriptions of the Upper Cretaceous of Mexico and its relations to the 

 Lower Cretaceous strata will be found, together with lists of fossils and correlations 

 with European divisions, in the "Guide des excursions" * of the tenth international 

 geological congress, at Mexico, in the following sections: 



No. 29. Environs de Monterrey et Saltillo. — Bose. 



No. 26. Geologic de la Sierra de Mazapil et Santa Rosa. — Burckhardt. 



No. 24. G6ologie de la Sierra de Concepci6n del Oro. — ^Burckliardt. 



No. 2,3. Excursion dans les environs de Parras. — Bose. 



No. 27. Les gisements carbonif&res de Coahuila. — ^Aguilera. 



G 12, H 11. LOWER CALIFORNIA. 



The "Mesa sandstones" of Lower Cahfornia, which were described by Gabb on 

 very slight evidence as possibly Miocene, are here assigned to the Upper Cretaceous 

 on the evidence of their similarity to the sandstone of that age which occurs at Ense- 

 nada. (See p. 647.) From Gabb's account of the peninsula ^^° we quote as follows : 



The three geographical divisions into which I have separated the peninsula are dependent 

 for their peculiar features on their geological structure. The rough mountains of the south are 



