28 GULF TERTIARY OF TEXAS. 



Fossils are very numerous, and many species resemble those of White Marl 

 Bluff, on the Colorado. In fact, it occupies the same stratigraphical position 

 at the base of the Fayette Beds, i. e., at the top of the fossil-bearing strata of 

 the Eocene. The next outcrop seen below this appears at the mouth of the 

 Little Brazos River, and is a representative of the Fayette Beds, which will 

 be described beyond. 



COLOEADO RIVER SECTION. 



Five miles by river below the outcrops of Basal Clays already described, in 

 the neighborhood of Webberville, is seen a low bluff, rising some four feet 

 above the water and a quarter of a mile long, composed of glauconitic marl 

 with many Eocene fossils. This represents the lowest f ossiliferous bed of the 

 Timber Belt series in this locality. From a point two miles below the Bas- 

 trop County line to the town of Bastrop is about twenty miles by river. In 

 this distance are seen numerous outcrops of gray sands, cross-bedded, and 

 containing black specks, which are often glauconite, as well as large concre- 

 tionary and indurated masses, like those already described on the Brazos 

 at Rocky Rapids. As at Rocky Rapids, they doubtless owe their existence to 

 the presence of argillaceous and calcareous matter, which has acted as a 

 cement. As already stated in the case of the Brazos River rocks, they are 

 simply hardened parts of the enclosing bed. Here, however, on the Colorado 

 they are much fewer and smaller (one to four feet in diameter) than on the 

 Brazos, and form a much less important part in the topography of the river 

 channel. The sand beds are frequently interstratified with beds of gray clay. 

 Many beds of lignite, one to five feet thick, are found cropping out in the 

 bluffs, and thin seams and lenticular masses of carbonate of iron are fre- 

 quently seen throughout the formation. This latter is generally partly de- 

 composed and exposes a rusty surface. Frequently it shows shrinkage cracks, 

 proving its once gelatinous condition. The dip of these sands and clays is 

 to the east and southeast at an angle of from to 5 degrees. The bluffs are 

 usually capped by from ten to thirty feet of Quaternary gravel and sand. 



From Bastrop down the river for eight miles a series of interbedded and 

 interlaminated gray, brown, and chocolate clays and sands is seen in many 

 bluffs. The seams of clay are often not over one eighth inch in thickness, 

 and yet they preserve a very remarkable continuity; the interlaminated sand 

 occurs as a series of connected lenses, and gives the underlying and overlying 

 clay laminae the characteristic undulating appearance. (See Figure 1.) 



