498 E. T. BUMBLE 



held by a barrier or the southeastward extension of the TamauHpas 

 Range and that part of its present coast in the vicinity of Tampico 

 was occupied by the waters of the Pacific. 



The observed facts indicate that during the Middle Eocene 

 the waters of the Atlantic occupied the territory north of the 

 Tamaulipas Range and the waters of the Pacific the region south 

 of that range, and that with the beginning of the Oligocene, the 

 waters of the Atlantic claimed both of these regions. It is there- 

 fore evident that the connection between the Pacific Ocean and its 

 Tampico embayment was closed entirely, either during the Upper 

 Eocene or at its close, and that the extension of the present Gulf 

 coast southward from Tordo Bay dates from this period. 



While the exact area embraced in this embayment south of 

 the Tamaulipas Range is unknown, its point of connection with 

 the Pacific Ocean was probably near the present Isthmus of Te- 

 huantepec and its western border was formed by the escarpment of 

 the Cordilleras. It is probable that its northerly extension occu- 

 pied the site of the valley now traversed by the railroad between 

 Tampico and Monterey. The Tamaulipas Range must have 

 formed its eastern boundary in this northern portion, but we have, 

 at present, no idea of its eastern limit farther south beneath the 

 western margin of the present Gulf of Mexico. It seems probable, 

 however, that this Tampico embayment was a body of water not 

 unlike the Gulf of California, both in extent and in trend, and that 

 it made a peninsula of that part of the Republic of Mexico north 

 of the Isthmus of Tehuantepec just as the Gulf of California now 

 makes the peninsula of Lower California. 



