MEMBERS OF THE AUSTIN SECTION. 323 



culminating horizon of Kingena (Terehratiila) wacoensis, Roenier. Exogyr-a 

 arietina, Roemer, and Gryphsea mucronata, Gabb, are found in these beds 

 only, in the mid- Texas sections, and mark a distinct fossil zone in the 

 Texas Cretaceous ; the other forms mentioned occur in underlying faunas. 

 This fauna is the upward limit of the grand fauna of the Washita divi- 

 sion, the sub-faunas of which show connection by a few common binding 

 species. On the other hand, not a single species passes upward from the 

 Exogijrd arietina beds into the Shoal creek (Vola) limestone, thus showing 

 between these beds a life-break as marked as is the lithologic change. 



To the southward of the Colorado these clays appear at various places 

 along the great Balcones fault at least as far as Del Rio, 200 miles south- 

 west of Austin, where they cross the Rio Grande in a bed of greatly in- 

 creased thickness. 



Northward from Austin the Exogyra arietina clays continue as far as 

 the Brazos and maintain the same relative position between the lime- 

 stones below and above. The medial limestone bands before mentioned 

 become thicker and more pronounced to the northward. North of the 

 Brazos the impure limestone bands increase in proportion to the clays 

 until, at Denison, the latter have entirely disappeared, probably by ero- 

 sion,* and the Main street limestone alone represents there the Exogyra 

 arietina clays and Kingena bed at Austin, and their respective faunas are 

 almost identical. 



While the Kingena zone at Austin lithologically belongs with the 

 underl3nng limestones (Shumard's Washita limestone beds, in part the 

 Fort Worth limestone of my former nomenclature) paleontologically its 

 afiinities are with the Exogyra arietina beds, as it continues to be the 

 base of this terrane to Red river, where it is part of the Main street lime- 

 stone, and is separated from the Fort Worth limestones by the interca- 

 lation of a great thickness of beds and faunas which apparently has little 

 or no representation in tlie Austin section. This is discussed more fully 

 under the head of the Denison section. 



Fort Worth Limestones. — The Exogyra arietina beds rest abruptly upon 

 a group of impure white limestones, of regular banding, and alternate 

 with marly clays— the Forth Worth limestones of my previous nomen- 

 clature. This name I now propose to restrict to the thicker, lower 

 beds, as shown in figure 3. This is the most conspicuous lithologic phase 

 of the W^ashita division. The following section and details of these beds 

 are noted : 



The strata of the lower- portion of the section is composed of thicker 

 alternations than the upper, although they all have the same w^hite color. 



*One mile east of Handley, in the Fort Worth section, the clays have a great thickness above 

 the Main street limestone. Both are here overlapped by Dakota. 



