78 A GEOLOGICAL SURVEY OF LANDS 



nearer to the marg-in of the basin in which the coal was made. 

 But we have no knowledge of the shape of the original basin. 

 There may have been irregularities in its outlines and areas may 

 exist in its marginal region wliere the vein is better. Rapid 

 changes of this kind are indicated hj the differences in the sections 

 of the tvyo pits made on the Olmos creek. There can be no doubt 

 that the vein is workable in manj' places in block 16 and also in 

 the surveys adjoining survey 166 in block 7. Changes in the 

 seams are characteristic of the outer margin of most coal basins. 

 The eastward extent of the coal beyond this can only be 

 determined by drilling, as exposures in that direction show only 

 the presence of the sediments which contain the coal. If prospect 

 holes were made near the tank on survey 193 in block 7, and near 

 the centre of survey 145 in the same block, and if no workablecoal 

 were found within 400 feet of the surface at these points, the ques- 

 tion would be settled. Eastward from the latter point the sedi- 

 ments change to such a degree that it is not likely any consider- 

 able veins of coal e.vist. The limits of the coal basin does not ex- 

 tend farther than this. The sea was apparently too open for the 

 accumulation of vegetable material in that direction. 



The Escondido beds. 



This name has been applied to all of thesedimentsofthe Eagle 

 Pass epoch overlying the coal series and beginning below with the 

 ledges which cap the bluffs a half mile east of Eagle Pass. The 

 thickness of these beds on the Texas side of the Eio Grande is 

 about 800 feet. They consist mainly of clays and marls of dark 

 color, interbedded with more or less extensive strata of sandstone, 

 limestone, and layers of oyster shells. The area where this divi- 

 sion of the Eagle Pass formation is exposed may be roughly indi- 

 cated as being the country east from Eagle Pass, nearly reaching 

 to Zavalla county and southeast as far as to Comanche creek and 

 a little beyond the north limit of the Antonio Rivas grant. 



An examination of the country shows that the sandy and cal- 

 careous stony ledges are arranged in essentially three groups: 1) 

 the basal sands, 2) the middle sands and 3) the upper sands, and 

 that each of these is overlain by more or less persistent^ developed 

 clay deposists, which may respectively be designated as the lower, 

 the middle, and the upper clay. It is also evident that this group- 



