LOWER CRETACEOUS. 587 



lenses. Occasionally beds of limestone of brecciated structure are found. In the lower part 

 there sometimes occur beds of limestone with chert concretions, but the upper part consists 

 generally only of gray limestone with interbedded dolomite. It may be said that these strata 

 everywhere contain Rudistes, especially radiolites. 



Bose then cites a number of localities. In regard to the Neo-Cretaceous (Upper 

 Cretaceous), he says that the strata of Tuxtla, Gutierrez, and Chiapa, which Sapper 

 took for Neo-Cretaceous, in reality belong to the Eo-Cretaceous; that he himself 

 has never observed strata which might with certainty be assigned to the Neo- 

 Cretaceous; but that possibly the dolomites arid limestones in the extreme north of 

 Chiapas represent a horizon of Upper Cretaceous. 



E 14. STATE OF VERA CRUZ, EASTERN SLOPE OF THE MEXICAN PLATEAU. 



C 



In the vicinity of Orizaba Bose *' made a special study of a Cretaceous section 

 which he divided into three parts, to each of which he gave a locality name. His 

 account may be summarized as follows : 



In the region which we are to describe and which includes the environs of the Rio Metlac 

 and Boca del Monte branch of the Veracruz-Mexico Railway the only sedimentary formations 

 that occur belong to the Cretaceous system. They have been divided into three parts, which 

 may be distinguished partly by paleontologic criteria and partly by lithologic differences. The 

 formations are, in succession from above downward: (1) Escamela limestones; (2) Maltrata 

 limestones; (3) Necoxtla slates. * * * 



The greater part of this division [the Necoxtla slates] consists of argillaceous slates which 

 are yellowish, gray, and reddish, with the luster of silk, and which include not infrequently 

 segregations of pyrite crystals. The slates also contain in some places small amounts of mica. 

 They are very fissile. In the upper part of the slates one may observe an enrichment in lime 

 and the slates are often arenaceous and sometimes merge into a greenish sandstone which 

 contains a large proportion of lime and in some places is almost entirely composed of calcareous 

 fragments. 



The Maltrata limestones constitute an important division, which is often of great thickness. 

 The greater part is composed of limestones in thin beds, is without fossils, and of a clear dark- 

 gray or black color. The limestones contain numerous segregations of flint in the form of 

 lenses. In the upper portion the flint occurs in the form of nodules and irregular bodies. In 

 the lower part of the limestones there occur in many places intercalated argillaceous slates 

 which are yellowish and lustrous like silk, but these never form heavy beds. In the upper part 

 toward the boundary with the Escamela limestones, there occur gray limestones and dolomites 

 in heavy beds in which the stratification is scarcely recognizable. Above these follow dark 

 compact limestones which represent the passage to the Escamela limestones and which may 

 better be considered a part of the latter. In some places there occur above the dolomites flinty 

 limestones, and in that case the line between them and the Escamela limestones is sufficiently 

 well marked. 



The Escamela limestones are composed of a clear gray to a dark-gray limestone, in some 

 places but slightly stratified and elsewhere in clearly distinct beds. Cherts occur only in the 

 lower portion. There are no intercalations of slates or marls. The limestones resemble in their 

 characters very often the Cretaceous limestones of southern Italy. They are petrographically 

 very uniform and may be recognized with ease. 



