488 E. T. BUMBLE 



MIDDLE EOCENE 



Buhrstone and Claiborne. — In the Alabama section the Buhr- 

 stone and Claiborne have a total thickness of about 450 feet, the 

 Claiborne proper being only one-third of this amount. The sur- 

 face exposures rarely exceed a total width of fifteen miles. In 

 Texas the narrowest portion of this Claiborne belt occurs on the 

 Colorado River and has a width of twenty-five miles, which widens 

 northeast to ninety miles on the Neches and attains a similar width 

 southwestward in the Rio Grande region. Along the Rio Grande, 

 which crosses the formation obliquely to the dip, the belt has an 

 exposure of 150 miles. The beds in Texas also have a correspond- 

 ingly increased thickness and have been divided as follows: the 

 Carrizo sands corresponding to the Buhrstone; the Marine, Yegua, 

 Fayette, and Frio substages — all of which carry fossils character- 

 istic of the Lower Claiborne. These substages are present from 

 the Conchos or Presas River in Mexico to the Colorado in Texas. 

 The Frio has not been recognized east of the Colorado, and east 

 of the Neches the Fayette is also wanting, except as isolated 

 patches, owing to pre- Jackson erosion. 



The Carrizo sands which mark the beginning of the Middle 

 Eocene deposition are the stratigraphic continuation of the Queen 

 City beds of northeast Texas. Throughout this region where 

 Kennedy first observed them, the relations of these sands to the 

 underlying Lignitic is such that he considered them to be the upper 

 member of that stage and so described them. Later examinations 

 in the western part of the state, however, brought out the fact that 

 the Carrizo sands were entirely unconformable with the Lignitic 

 deposits and that in some locahties they grade upward into the 

 basal beds of the Marine substage. 



In Northeastern Texas the Carrizo sands have a thickness of 

 70 feet and appear to be conformable with the Lignitic. On the 

 Atascosa the contact was not observed^ but the sands were appar- 

 ently of much greater thickness. On the Rio Grande the beds 

 are exposed over a very wide area, outcropping alon^ the river for 

 a distance of forty miles. They have a less marked dip than either 

 the Lignitic or Midway and are found resting on both of these and 



