118 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



of the fossils appear to belong to the Miocene. Near Macus- 

 pana and elsewhere in Tabasco he found beds containing fossils 

 which he referred to the Marine-Pliocene. 



Engerrand describes the fossils from Zuluzum near Palenque 

 in Chiapas, which he regards as Miocene. 



The beds occurring on the Isthmus of Tehuantepec (outside 

 a small exposure of the rudistes limestone) carry an abundant 

 fauna, but the specimens are not well preserved. The deter- 

 minations of species by Dall, Toula, Bose and others and their 

 conclusions as to age, while appearing to agree on the Pliocene 

 or later age of these deposits, seem to indicate that a portion 

 of them may be older than this reference. This is apparently 

 sustained by Bose®, who found similar beds at Santa Maria 

 Tatetla, northwest of Veracruz, from which he described a 

 number of species as Pliocene but later states that since larger 

 and more careful collections have been made he considers the 

 age to be Miocene. 



It will, therefore, be seen that while Eogene fossils were 

 recognized north of the Tamaulipas range in the district of San 

 Jose de las Rusias, and both Eogene and Neogene sediments 

 found south of the Isthmus of Tehuantepec, nowhere within 

 the area of the Tampico Embayment were Tertiary deposits 

 observed which were referred to horizons earlier than the 

 Miocene. 



This was the condition when the oil geologists began opera- 

 tions. 



In Science of February 10, 1911, Dumble, reporting on the 

 results of two years' work in Northeastern Mexico, reports 

 the discovery of Oligocene deposits at San Fernando on the 

 Conchos River and in the San Jose de las Rusias region and 

 suggests the probable Cretaceous age of the blue shales under- 

 lying the San Fernando beds of the Oligocene in the Panuco 

 district, which in turn were succeeded by later beds as seen at 

 Tuxpam. 



In 1910 Jeffreys made a report on the geology of eastern 

 Mexico which, while it may not have been published, has been 

 the basis of much that has been written by others. In this re- 

 port he takes the same view of the age of the deposits in this 

 area as that stated above. 



•Bull. 22, Mex. Geol. Comm. 



