492 E. T. DUMBLE 



south, while in the eastern portion of the state the lagunal and 

 swamp conditions apparently predominated. 



There are unconformities here and there and evidences of local 

 warping of the strata in the various substages, but they are, never- 

 theless, bound together by transitional beds or identity of fossils. 



The constantly changing conditions of deposition in the region 

 east and north of the Tamaulipas range during Middle Eocene 

 time, as shown by the variableness of the deposits above described, 

 did not extend to the region lying west and south of that range. 



West of the Tamaulipas Range the blue shale of the uppermost 

 Cretaceous is followed by other shales so similar in general char- 

 acter that only the finding of Eocene fossils in them suggested the 

 differentiation of the two. 



The only localities where exposures of these beds have certainly 

 been found is in the vicinity of Alazan, on the Buena Vista River, 

 about twenty-five miles northwest of Tuxpam. 



The deposits are bluish shales that weather white or yellow and 

 their exact relations to the Cretaceous were not determined, on 

 account of the inadequate exposures. The fossils are widely 

 scattered through the shale and it is possible to collect them in 

 good condition only from decomposed fragments of the rock. 



This locality was discovered by Mr. DeGolyer and fossils 

 found by him were recognized by Dr. Dall as Pacific Coast forms. 

 It was afterward visited by Professor Cummins, who made a some- 

 what larger collection of the fossils. These were also submitted 

 to Dr. Dall and afterward turned over to Professor Roy E. Dicker- 

 son for study in connection with other Pacific Coast faunas of 

 Eocene age in his work at the University of California. 



The collection of fossils made at this locality by Professor 

 Cummins comprises a fauna consisting principally of gasteropods 

 and small bivalves. The preliminary examination failed to show 

 any forms which could be referred to our Claiborne, but did show 

 some that were apparently identical with, and many that were 

 very similar to, Eocene Tejon of California. 



These beds dip eastwardly and probably extend some distance 

 north and south of Alazan. Shales similar to these were observed 

 along the railroad north of the Panuco River and on the San 



