20 GULF TERTIARY OF TEXAS. 



shells of Lower Eocene fossils. It is traceable up and down Rocky Cedar 

 Creek for seven miles, and underlies the divide between Rocky Cedar and 

 Muddy Cedar creeks, a distance of four miles. The following section of a 

 well on this divide shows the character of this bed. 



1. Sand, gray and buff color 3 feet. 



2. Gray and yellow clay (Basal Clays) ..... 9 feet. 



3. Shell limestone 3 to 4 feet. 



4. Coarse sand H to 2 feet. 



5. Shell limestone ■ 3 to 4 feet. 



6. Sand in bottom of well. 



About a mile below the point where the Texas Pacific Railroad crosses 

 Rocky Cedar, an outcrop fifteen feet thick of this limestone is seen, and as 

 it still forms the bed of the creek, its thickness here must be still greater than 

 that. The divide between Rocky Cedar and Muddy Cedar is covered with 

 sand as shown in the above section, and is heavily timbered with oak and 

 hickory. The village of Elmo is situated on Muddy Cedar, and just beyond 

 it we come into a black prairie region showing Cretaceous fossils. Conse- 

 quently the Rocky Cedar limestone is probably the lowermost bed of the Ter- 

 tiary series in this part of the State, and the line of parting between the Cre- 

 taceous and Tertiary strata can safely be placed about at Elmo, or possibly a 

 little west of it. The shell limestone bed is probably of limited extent, occu- 

 pying no very important stratigraphical position, and appearing at the base 

 of, and as a component part of, the Basal Clays. It is of great importance, 

 however, as showing the geological position of the lowermost Tertiary strata 

 in Northern Texas. The Basal Clay bed in Bastrop County is seen to the 

 west of Elgin, and between there and Manor, in Travis County. It forms 

 the same character of country as in the northern part of the State, and fin 

 ally disappears to the east under the overlying sands. On the Colorado River 

 it is seen cropping out at a point sixteen miles by river below Austin, and 

 one mile below the mouth of Onion Creek, in a bluff some forty feet high and 

 a mile long. Also at Webberville, on the line between Travis and Bastrop 

 counties, where it is seen in a low bluff just above the water's edge. This is 

 a much darker and more massive clay than that seen in most other outcrops. 

 In the bluff sixteen miles below Austin are found a few fragments of fossils, 

 but they are all so broken as to make their determination very doubtful. The 

 representative of this bed on the Brazos is seen in the bluff s of the river ex- 

 tending from the northeast corner of Milam County down the river to within 

 two miles of Pond Creek, a distance of about seven miles. These clays here 

 overlie the "Ponderosa Marls" which are extensively developed between this 

 point and Waco. They differ somewhat in lithological character from the 

 clays at Wills Point, and are at many places highly fossiliferous. The first 



