46 GULF TERTIARY OF TEXAS. 



1. Indurated light brown sand 3 to 6 feet. 



2. Loose light brown sand 10 feet. 



3. Gray clay 5 feet. 



4. Oyster bed, Ostrea georgianal. . . 10 to 12 inches. 



5. Gray clay 1 foot 



6. Oyster bed, Ostrea georgianal 1 foot 



7. Detritus to water edge 4 feet. 



Beds 4 and 6 are a solid mass of shells. Some of the oyster shells are over 

 one foot long. Dip of strata varies from horizontal to 3 degrees northeast. 

 Eight miles above Roma are seen similar beds, associated with similar clays, 

 and dipping 2 to 3 degrees south. Two miles below this point, on the Mexi- 

 can side of the river, the following section w T as seen: 



1. Greenish-yellow hard clay, with white calcareous concretions, gypsum, and 



sulphur, indurated in layers one to three inches thick. 20 feet. 



2. Oyster bed, same as described above, in a white calcareous rock 2 feet. 



3. Same sands and clays as in 1 18 feet. 



4. Brown and black lignitic clay, with gypsum and sulphur 6 feet. 



5. Siliceous sandstone, rusty and hard in seams, gray to brown in color, and con- 



taining much sulphur as it approaches bed 4 10 feet. 



Dip of strata 7 degrees southeast 



The bluff varies from ten to thirty feet in height, and is a half mile long; 

 the above section is taken along three hundred yards of it. Two miles below 

 this, on the Mexican side, is seen an oyster bed, in the same associations as 

 in the above section. It is ten feet thick, and contains a seam of clay in the 

 lower part. The bed immediately overlies the brown and black clays of the 

 last section. Dip, to 2 degrees northwest. Four miles below, on the Texas 

 side, are seen ledges and reefs of similar shell beds, and in some cases single 

 shells are as much as eighteen inches long. Dip, 5 degrees west. The same 

 formation runs hence to Roma, but at that place only a few of the large 

 oyster shells are seen scattered through the buff sandstone. One and a half 

 miles below Roma are seen the same strata as at that town, and dipping 7 

 degrees east. At this point we come into a great clay and sand area, non- 

 fossiliferous, and resembling the Fayette beds ("Grand Gulf") of the Colo- 

 rado River. It seems exceedingly possible, however, that the oyster-bearing 

 strata above and below Roma, and even some of the beds as far up as the 

 mouth of the Salado and above in the isolated localities mentioned, may come 

 under this head. They resemble the Fayette Beds very much in lithological 

 character, and all contain the characteristic clays of that epoch. The large 

 oysters mentioned above have not been found in East Texas, and therefore 

 the strata containing them must either be wanting there, or must represent 

 the base of the "Fayette Beds" of that region. Another argument in favor 

 of the supposition of the extension o± the Fayette Beds up the river is that if 



