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



observed again north of Venezuela, 2,000 miles away. Fossils 

 of the Lower Claiborne occur along the Conchos River not 

 more than 30 or 35 miles from the upper end of the Embay- 

 ment area, near Linares, but are not known farther south. 



The waters of the Eocene sea covering the Tampico Em- 

 ba}Tnent area probably came in from the south and were either 

 entirely separated from those of the Gulf or their connection 

 was such that the faunas did not mingle. 



Toward the close of the Middle Eocene further elevation 

 and folding took place. This is shown in the Pomeranes 

 Mountains north of the Conchos River, in the mountains east 

 of Burgos, south of that stream, at Alazan, and at Chicontepec. 

 This movement is also evidenced on the Texas coast by the ab- 

 sence of the Upper Claiborne and the erosion of a part of the 

 Lower Claiborne prior to the deposition of the Upper Eocene 

 or Jackson. 



The succeeding submergence clearly shows a connection in 

 the Embayment area of the waters of the Pacific and those of 

 the Atlantic by the commingling of the Pacific and Gulf types 

 of fossils at Alazan where Tejon forms of the west are mingled 

 with Jackson and possible Upper Claiborne forms from the 

 Gulf. 



The close of the Eocene was marked by further folding, ele- 

 vation, and erosion. 



The Oligocene submergence, which followed, seems to have 

 afifected not only the entire Gulf region, but the Carribean as 

 well, and since almost identical faunas are reported from the 

 west coast of Mexico, it is probable that the passage between 

 the Oceans was still open. 



With the final emergence of the Oligocene* important sedi- 

 mentation in our area seems to have ceased, and was succeeded, 

 probably during the Miocene, but, seemingly, before any great 

 erosion had taken place, by the vulcanism which gave us the 

 dikes, necks, and caps of basalt. 



To the north and south of this area the coast was subjected 

 to further submergence and deposits of Miocene and Pliocene 

 age were laid down, but such Post-Oligocene submergences as 

 may have occurred in this portion of the Tampico Embayment 

 area seem to have been relatively unimportant. 



* The nummivlitic limestones of the San Rafael beds are ample warrant for their 

 reference to the Oligocene. The Tuxpain beds were included in the Oligocene because 

 of the identity of certain ferns. Some of these ferns, however, seem to indicate a 

 later horizon and closer collecting may necessitate a reference of the Tuxpam beds 

 to the Miocene. 



