44 GULF TERTIARY OF TEXAS. 



1. Oyster bed, containing fragments of oysters cemented in greensand marl 1-2 feet. 



2. Softer greensand marl, with a few oysters, Turritella, shark teeth, etc 2 feet. 



3. Interlaminated gray and chocolate sandy clay with sulphur 2 feet. 



4. G-reensand marl to water edge ... l-£ feet. 



Below this point for five miles similar deposits are seen, and here we come 

 to another highly fossiliferous bed consisting of interbedded siliceous sands, 

 chocolate clays, and greensand, in a bluff fifty feet high. Half way up is a 

 bed composed mostly of shells in a greensand matrix, and eight to twelve 

 inches thick. In it were found many oysters, Turritella and other gastero- 

 pods. Hard gray calcareous nodules, like those at "Bombshell Bluff," on the 

 Colorado, and containing specks of lignite, are found throughout the section. 

 One mile below, and on the Mexican side, is a bluff thirty to fifty feet high, 

 and extending down the river for a mile and a half. It is composed of inter- 

 bedded gray sands, with specks of glauconite, and chocolate and gray clays, 

 containing thin lenticular seams of lignite one-eighth to one-quarter inch 

 thick, and a few fragments of shells; also gray calcareous concretions one to 

 two inches in diameter, and gypsum crystals. At its lower end this bluff 

 runs into a somewhat similar formation, but differing from it in having many 

 colored sands in seams of purple, red. yellow, brown, and bluish-gray. Con- 

 siderable quantities of iron pyrites are present, and it is probably to this that 

 much of the coloring matter is due. Two. miles below here the strata again 

 assume their normal character, and dip two degrees southeast. About at the 

 line between Webb and Zapata counties is a bluff a mile long, and reaching 

 a maximum height of a hundred feet. It consists of buff and greenish- 

 colored sands with gray calcareous concretions, one to ten feet in diameter, 

 and many large gasteropods, one to four inches long, in a hard shell rock at 

 the base. Near the top of the bluff is another shell bed, six to eight inches 

 thick, lenticular, and made up mostly of fossils, among which are many Tur- 

 ritella and Cardita. Similar bluffs, but without fossils, are seen almost con- 

 tinuously down the river, on the Texas side, for two miles. 



At the mouth of Arroyo Dolores are found glauconiferous beds with many 

 oysters, in places made up entirely of them, with apparently no other fossils, 

 and rising ten to thirty feet above the water. Thirteen miles above San Ig- 

 nacio is seen a low reef of hard gray limestone, weathering to a greenish-gray 

 color, and rising two feet above the water. It shows a concretionary struc- 

 ture in places, and forms rapids in the river. Four miles below this is a bluff 

 three hundred yards long and varying from twenty to sixty feet high. The 

 upper third of it is composed of river alluvium, with a pebble bed at its base. 

 The lower part consists of buff sands and sandstones, with seams of chocolate 

 clay and greensand. The top of this deposit is capped by a shell bed containing 

 glauconite, and six to eight inches thick. Among the fossils were found 



