JURASSIC. 551 



of bright-red and greenish tints which suggest the European Triassic as well as some 

 Jurassic clays. As they are unfossiliferous their age is not determinable. Above 

 them lies a great thickness of calcareous and in part marly deposits, which are 

 without doubt of Jurassic age. They include dense light-gray limestone which 

 appears in general to be unfossiliferous with the exception of the remains of a small 

 Exogyra that could not be more exactly determined. Above this lower sequence 

 outcrop certain marly strata which contain numerous thin lenses of brown iron ore 

 and which like the preceding are very poor in fossils. They have yielded an impres- 

 sion of an Apiocrinus stem and an ainmonite, Stephanoceras paucicostatus. This 

 species belongs to a group of the ammonites whose youngest representatives do not 

 range above the Oxfordien, and the marls therefore belong either to that horizon 

 of the white Jura of Europe or are to be assigned to the brown Jura of Europe. 



The crest of the Cerro Titania is formed by gray marly limestone which is 

 highly fossiliferous. The character of the contained fauna is that of the white Jura 

 ^nd probably represents the European Sequanien. 



E-F 14. PTJEBLA AND VERA CBTJZ. 



According to Felix and Lenk ^^^ the late Mesozoic is represented in the states 

 of Puebla and Vera Cruz by fossiliferous strata containing fauna related to that of 

 the Lias (Lower Jurassic) of Europe. Most of the specimens found belong to 

 Arietites jamesdanae Barcena, and are as a rule but poorly preserved. The rock is 

 a black to yellow clay slate whicii contains no lime but which on the other hand 

 includes plates of mica and is somewhat metamorphosed, so that it resembles 

 Paleozoic rocks rather than Mesozoic. 



Felix and Lenk give a list of nine localities at which fossils have been found. 

 The Lower Jurassic strata are overlain by black calcareous slates interbedded with 

 black limestones that contain Perisphinctes and are assigned to the Upper Jurassic. 

 These in turn are followed by limestones of the Lower Cretaceous. According to a 

 section through Barranca de la Calera and Barranca del Rio Potrero Seco, both in 

 Vera Cruz, by Bose, the strata are conformable from Lower Jurassic to Lower 

 Cretaceous. 



F 14. SIERRA DE CATORCE, SAN LTJIS POTOSI. 



Felix and Lenk ^^''* state that the Jurassic is widely distributed in Mexico but 

 does not appear anywhere to form areas of great extent. The occurrences are 

 small in area and widely separated, and they are also notably different in faunas. 



In the Sierra de Catorce, in San Luis Potosi, certain unfossiliferous gray slates 

 are succeeded by late Mesozoic strata which have been separated by Castillo and 

 Aguilera "^ into two divisions, and the lower of these has been again divided into 

 two terranes — an upper one, the Cieneguita, and a lower, the Alamitos. 



The Alamitos formation consists of fine sandstone and marly or clayey slate 

 interbedded with each other. It contains numerous fossils, a Ust of which is given 

 in both of the works cited. The Cieneguita formation also consists of marly slates 

 and sandstones which contain more or less carbonate of lime. A number of fossils 

 have been found. The upper of the two major divisions contains in the upper 

 part ash-gray compact limestones which are more or less siliceous. The lower part 

 is shaly and the whole is very poor in fossils. The Alamitos and Cieneguita forma- 



