LOWER CRETACEOUS. 591 



stones with black chert, having a thickness of 400 to 500 meters or more. In the 

 vicinity of Cohma there are limestones and shales. On the eastern slope of the 

 Sierra de Tamaulipas, near Victoria, occyr limestones and shales. 



In the State of Chihuahua the transition stage to the Cenomanian occurs at 

 several places in the Cerro Muleros, near Ciudad Juarez, with argillaceous sand- 

 stones and shales, and at Encantada, near Placeres de Guadalupe, where there are 

 shaly limestones and marly schists. This stage corresponds to the Fredericksburg 

 group, or some portion of it, of the Lower Cretaceous of the United States. At 

 Arivechi, in the State of Sonora, there are calcareous and marly shales. 



The Cenomanian is weU developed throughout in the States of Chihuahua 

 (Cerro de Muleros) and Coahuila (Hacienda de Vacas, Rancho de San Diego, Santa 

 Eulalia, Javal, etc.), consisting of limestones and gray compact shales with a littoral 

 facies and a rich fauna. Characteristic fossils occur in the limestones and shales of 

 the Sierra Mojada. 



For the Neo-Cretaceous (Upper Cretaceous) see Chapter XV (p. 644) . 



, F 14. SAN LUIS POTOSI. 



In examining the section along the railway line between San Luis Potosi and 

 Tampico, Bose *^ studied a Cretaceous series which is distinguished by a peculiar 

 facies that is not represented as a whole elsewhere in North America, except 

 perhaps in Jamaica. He has described the fauna and correlation in detail. The 

 following statement regarding the stratigraphy is extracted from his work : 



The strata which contamed the fauna described in this work constitute a complete whole 

 to which we give the local name Cardenas division, for the facies is very different from that of 

 any other Cretaceous formation in America. It has a sufficiently great thickness, which may 

 be estimated approximately at 600 meters; tliis amount is naturally not exact, as the strata 

 have been greatly folded, and it has not been possible to establish with certainty the existence 

 of any younger beds. Lithologically, the Cardenas division is composed of various formations. 

 Above the heavy-bedded limestones which form the canyon of Tamocopo, in the upper portion 

 of wliich we have not been able to find determinable fossils, there occur in the vicinity of Canoas 

 station arenaceous limestones, which alternate with marls and with clay and marly slates. 

 Above these slates occur heavy beds of limestone, wliich are in part marly, and still higher there 

 again appear marly and arenaceous slates, which pass gradually into heavy-bedded limestones. 

 These are poor in fossils and are followed at first by yellow clay slates without fossils, upon wliich 

 rest marly yellow slates with intercalations of sandstones of the same color, which are fossilifer- 

 ous. The top of the division is composed of marls of a grayish- j-ellow color, with some beds of 

 limestone. The beds are very strongly folded and their order of succession can not be made out. 



Stanton*^ states : 



Near the eastern margin of the Mexican plateau, between San Luis Potosi and Tampico, 

 there is a thick Cretaceous section wliich evidently includes the equivalent of a large part of the 

 Comanche series as well as some Upper Cretaceous. A part of the latter which shows a faunal 

 and hthologic facies not known elsewhere in North America has been described by Bose under 

 the name Cardenas division and referred to the lower Turonian. Its thickness is estimated at 

 600 meters. The presence of Exogyra costata and Gryphsea vesicularis suggests its approximate 

 correlation with the Ripley of the Southern States, but the rest of the fauna is distinct and in 

 its general character more nearly resembles that of Jamaica and of the European Gosan beds. 



"■ Personal commumcation. 



