EOCENE HISTORY OF MEXICAN CULF COASTAL AREA 493 



Antonio River west of Cruz, a station on the railway between 

 Tampico and Monterey. Cummins correlates these shales north 

 of Panuco and west of Cruz with the Alazan deposits because of 

 common lithological character, although he found no fossils in 

 them. 



They were, however, certainly found in drilling a well at Topila, 

 on the Panuco River, at a depth of 1,810 feet, as shown by the 

 fossils brought up with the drill. Of the fifteen species collected 

 at this locahty nearly one-half are identified as Tejon species and 

 the others as nearly related to them.^ 



UPPER EOCENE 



So far we have not positively recognized the Frio clays, which 

 are the uppermost beds referable to the Middle Eocene, east of the 

 Colorado. Other beds of clay have been referred to this substage, 

 but closer investigation seems to show that the Frio clays are not 

 present in eastern Texas. Growing out of such correlation it has 

 been presumed that both the Fayette and Frio of eastern Texas 

 are later than the Lower Claiborne and correspond with the Jackson 

 and the Oligocene. 



In the area west of the Colorado River, where these beds have 

 had closest study and where they are most fossiliferous, it is very 

 certain that this presumption is erroneous. There is a continuity 

 of the Lower Claiborne fauna through these upper beds and no 

 forms whatever of Jackson or later age have been observed. 



In all this area the Frio is found resting seemingly upon an 

 uneroded surface of Fayette sands and north of the Rio Grande it 

 is unconformably overlain by the Oakville Miocene without b'eds 

 of either Upper Eocene or Oligocene age intervening. 



East of the Guadalupe River the conditions are somewhat 

 different. In the valley of the Colorado and eastward to the 

 Sabine it is evident that subsequent to the deposition of the Frio 

 and prior to the beginning of Jackson deposition as now known, 

 there was a period of erosion during which the Frio, more or less 

 of the Fayette, and even a part of the Yegua were carried away. 

 This erosion probably took place during the deposition of the Upper 



' Science, XXXV, 906-8. 



