72 A GEOLOGICAL SUBVEY OF LAXDS 



exploration. But indications do not warrant drilling for this 

 exclusive purpose. It would seem wise to closely watch any drill- 

 ings which may penetrate this limestone, as in block 9 and in the 

 north part of block 1 and block 3 in Maverick and Zavalla 

 counties. 



THE EAGLE PASS FORMATION. 



Like all the sediments previously described, the Upson clays, 

 when followed southward, disappear under later deposits. The 

 sediment overlying the Tpson clay have been called the Eagle 

 Pass formation. This consists of a series of clays, marls, sand- 

 stones and limestones, which include the coal now mined north of 

 Eagle Pass. The Eagle Pass formation presents two phases. 

 East of Chacon creek it is much thinner than west of this stream, 

 and contains but a few ledges of sandstone, while to the west and 

 south af a line nearly coinciding with the course of this stream 

 the formation is much thicker and sandstones and coal beds have 

 a greater development. Three fairly well marked divisions have 

 been made out along the Eio Grande, but these merge as we 

 approach the Chacon. Clearly the belt which separates these 

 two phases was a line which marked some geographical limit in 

 the Cretaceous sea, already at the time when the underlying Up- 

 son clay and the Anacacho limestone were being formed. The 

 country which is east of the Chacon must have been in a part of 

 the sea where sediments were less copious than to the west. It 

 was farther out in the sea than the region to the west, for here 

 we find more sandy deposits and also coal seams which are de- 

 rived from the vegetation near the adjacent land. 



It will be convenient to describe separately the clayey sedi- 

 ments to the east. On the Nueces these are known asthePulliam 

 formation from their exposures near the Pulliam ranch. Beginning 

 below, the three divisions of the Eagle Pass Formation west of 

 Chacon creek are: 1) The San Miguel beds, 1) the Coal series, and 

 3) the Escondido beds.* 



The San Miguel Beds. 



In the bluffs on the south side of Hack berry creek in surveys 

 70, 70y2, and 71J^ in block 4, the lowermost ledges of sand- 

 stone of these beds cap the Upson clan's. These sandstones are 



* Desiffnation first given by E. T. Dumble. 



