IN THE UPPER RIO GRANDE EMBAYMENT IN TEXAS. 65 



dred feet frequently include beds of marly shale and clay, in which 

 a most perfect lamination appears. These may be greenish blue 

 in color or dark gray or rusty red. At times they are black, 

 from bituminous or carbonaceous materials, or there may be 

 thin and flaggy straight layers of alternating lighter and darker 

 color. The upper half af the formation is usually free from clayey 

 layers, its stratification is more uniform and the ledges contain a 

 less amount of the fine sand. The rock becomes somewhat softer 

 and is more frequently white. In weathering, the Eagle Ford 

 beds invariably break into long quadrangular blocks, whose 

 length may ten times exceed their width or thickness, and whose 

 square edges have a tendency to weather to acute angles. Ferrug- 

 inous material is present in varying quantit3\ The lower strata 

 are sometimes stained bright red by oxide of iron, while in the 

 higher strata the same substance is present in clusters of cubic 

 crystals which originally were pyrite. These vary in size from 

 one eighth of an inch to three inches in diameter. 



Geographic Distribution of Outcrops. 



The siiicious and ferruginous ingredients in the Eagle Ford 

 beds render them somewhat more resistant to weathering than 

 most of the Cretaceous rocks in the Rio Grande embayment, and 

 we therefore often find them on the divides forming the highest 

 ground in the uplands. In the Devil's river countrj^ they have 

 mostly been worn away, but remnants of the basal part cap 

 many of the hills in the divides between the upper branches of 

 Deadman's creek, Evans creek, and Barranco Blanco creek and 

 also on the plateau north and east of California creek. In this 

 region the ferrugions material is quite abundant and the rock is 

 often of a bright red color. East of Del Rio some patches were 

 noted in block 4. In block 5 it is everywhere present on the up- 

 lands. In the south half of block 3 and in the north half of block 

 2 it forms most of the high divides. From the south half of block 

 11 the area of outcrop of this rock turns southeastward and 

 passes a broad belt between Pinto mountain and Brackett, sur- 

 rounding Elm mountain and extending on the south side of 

 Turkey mountain into Uvalde county. 



Bituminous Contents. 



In the lower part of this formation the shaly ledges are 

 occasionally impregnated with bitumen and oil. I find that some 



