Vol. V] DUMBLE— TERTIARY DEPOSITS IN NORTHEASTERN MEXICO J/J 



Around Cardenas, which is on the table-land east of San 

 Luis Potosi, overlying the Tamasopa limestones there are 

 highly fossiliferous beds which apparently represent the 

 Eagle Ford, Austin and part of the Taylor, as these forma- 

 tions exist along the Rio Grande southeast of Del Rio. 



In the Coastal plain of Mexico, east of the Cordillera, the 

 place of these fossiliferous beds is occupied, as has been 

 stated, by the San Juan and the non-fossiliferous Papagallos, 

 and these two formations stretch northward to the Salado 

 River bevond which we find again the fossiliferous beds of 

 the Upper Cretaceous. They, therefore, in all probability 

 either represent the deeper sea deposition of which the fossilif- 

 erous beds were more nearly littoral or indicate the existence 

 of a barrier of some description in this vicinity during the 

 later period of the Upper Cretaceous. The evidence seems to 

 favor the latter condition and that at the close of the Cre- 

 taceous this barrier was extended to the southeast by an up- 

 lift or uplifts which formed the series of mountain groups 

 and ranges here referred to as the Tamaulipas Range. 



On the Rio Grande there appears to be only a slight angu- 

 lar unconformity between the Cretaceous and the Tertiary, 

 but, going southward, we observe that the disturbances at the 

 close of the Cretaceous folded and flexed the limestones and 

 shales so that the contacts from Rodriguez south show very 

 decided unconformities. 



CRETACEOUS-TERTIARY CONTACT 



The contact between the Cretaceous and the Eocene which, 

 beginning south of San Antonio, Texas, runs a little south of 

 west to the southwestern portion of Uvalde County, makes 

 an abrupt turn at that point and then runs almost due south 

 for more than 250 miles to the Salinas River. From this 

 point it turns southeastward to the Conchos which flows for 

 miles along the southern boundary of the Eocene deposits. 

 The contact between the Cretaceous and the Eocene in Mexico 

 was first found on the Arroyo Caballero, a small creek 

 which empties into the Rio Grande on the Mexican side 

 some three or four miles north of the Maverick- Webb County 

 Line in Texas. From this point the contact runs southwest 



