Vol. VIII] DUMBLE-GEOLOGY TAMPICO EMBAYMENT AREA 139 



bands are fine-grained clay shale, dark blue gray to red in color, 

 and seeming to carry little or no sand in its composition. 

 Others, on the contrary, are very sandy, and in some places, 

 grade into a shaly sandstone with calcareous cement. No fos- 

 sils were found here." 



These shales occur here in gently undulating beds with pre- 

 vailing dips of one to four degrees a little west of south. 



These are apparently very similar to the shales called Mendez 

 by De Golyer. 

 ' Blue shales were also observed on the Tuxpam River, west of 

 Tumbadero. and near the coast as far south as the Arroyo 

 Hondo, between Tecolutla and Nautla, and at many other 

 localities in this region. 



Just how far south these Chicontepec beds extend cannot be 

 told at present, but they probably skirt the foot of the Cordil- 

 leras as far south as Nautla. 



Bose does not appear to have recognized any beds referable 

 to them in his Orizaba section. 



In Chiapas, however, he finds similar beds, and states that 

 the fossiliferous Eocene there consists of sandy shales, sand- 

 stones, clay shales, calcareous shales and limestones. The pre- 

 vailing colors are red and yellow, although sandstones, shales, 

 and limestones are occasionally gray or blue. 



The Eocene fauna of this region, like that of the Chicontepec 

 beds, appears to be almost altogether foraminifera— nummul- 

 ites and orbitoides. The nummulites are found scattered over 

 a considerable area, but the orbitoides were only found in a few 

 localities. Dr. Paul Oppenheim, of Berlin, identified them as 

 Orbitoides orthofragmina, a typical Eocene form. 



Therefore, so far as our present observations go, Lower and 

 Middle Eocene deposits such as occur in the Texas Gulf Coast 

 region are not found on the Mexican coastal region south of the 

 old barrier now represented by the Tamaulipas Range. Such 

 deposits as do occur in the Mexican region, and which may 

 represent the time equivalents of these Texas beds, are charac- 

 terized by an entirely different fauna. 



The succeeding Eocene beds as seen at Alazan are, appar- 

 ently, unconformable on the Chicontepec. The fauna is a 

 commingling of species occurring in the Tejon formation of the 

 Pacific Coast with those of the Upper Claiborne and Jackson, 

 or Upper Eocene, of the Gulf region. It has only been recog- 



