22 University of Texas Bulletin 



Paso. A line connecting these two areas will give very roughly the boun- 

 dary between the marl and lime areas. 



Sand faciet: 



Unknown. 



Clay facie*: 



Unknown. 



Marl facie*: 



Cerro de Muleros, near El Paso, gray to bluish marls ; Denison and east- 

 wards, marly limestone and marly interbedding. 



Limestone facie*: 



South of the Red River and throughout North and Central Texas at the 

 outcrop. The middle portion of the Georgetown limestone represents this 

 facies. A deeper sea subphase found in southern Trans-Pecos Texas con- 

 sists of hard, crystalline, sparsely fossiliferous, relatively pure, fine grained 

 lithographic limestone, which composes most of the Georgetown and Buda. 

 This is the purest and probably the deepest sea deposition known for this 

 formation. 



DUCK CREEK (Upper) 

 Sand facies: 



Unknown. 



Marl facie*: 



This group of strata is prevailingly a calcareous marl and contains the 

 least limestone at Gainesville. At Fort Worth it has only slightly more 

 lime than at Gainesville, while at Denison and at Caddo, Oklahoma, it is 

 distinctly more limy. The change from marliness to liminess therefore 

 appears to be in this region at least largely an east- west change. The 

 Duck Creek marl thickens to the northwest, being thickest near Denison 

 and thicker in the Tishomingo than in the Atoka area. 



Limestone facie*: 



South of the Brazos-Colorado River divide, the Duck Creek marl is im- 

 bedded in the base of the Georgetown limestone, where it is a marly im- 

 pure limestone. 



The situation in West Texas is unknown. 



DUCK CREEK (Lower) 

 Sand facies: 



Unknown. There are some bituminous sandy layers in the Duck Creek 

 in Cooke County, Texas, but these appear to be local. 



Shale (clay) facie*: 



Seen at the type locality, three miles north of Denison, Texas. This 

 shale is somewhat calcareous and is transitional to a marl. 



