54 University of Texas Bulletin 



does not imply that in certain formations no pyrite faunae will be found ; 

 they existed somewhere during the whole Washita at least, and likely will 

 be found in the clay facies of each formation, just as representatives of 

 the Mainstreet pyrite fauna have been found in the clay facies (Del Rio) 

 of Central Texas, though apparently absent in the limestone of North Texas. 

 It is certain that exuberant pyrite faunae are associated with clay facies ; 

 and accordingly the greatest abundance of pyrite fossils in the Kiamitia 

 is in southern Tarrant and Johnson counties ; Denton formation, Denison 

 to northern Tarrant County; Pawpaw formation, Tarrant County; Main- 

 street formation, McLennan County and southward ; middle Grayson form- 

 ation, Denton County. In each instance the lithology of the region men- 

 tioned is largely of the clay facies. These facts suggest recurrent similar 

 conditions which favored the spread of pyrite faunae. At a given locality 

 this recurrence might be many times repeated ; and such pyrite zones are 

 still being discovered at new stratigraphic levels. What these conditions 

 and their causes were will not be discussed here. They resulted in each 

 zone in a highly characteristic pyrite and limonite fossil association, which 

 is as follows: Area washitaensis, Engonoceras sp., Scaphites spp., Tur- 

 rilites spp., Hamites spp., Cinulia sp., Nerinea sp., Lunatia sp., Turritella 

 sp-, pyritic starfishes, and abundant small, non-pyritic Crustacea, especially 

 crabs. 



KIAMITIA CLAY FAUNA 



The marl facies of the Kiamitia formation extends from Primrose, 

 southwest of Fort Worth, to a point between Gainesville and Fink, on 

 the Red River. The clay facies extend from near Primrose to at least 

 the Brazos River ; it is found throughout Johnson County, and on Cedar 

 Creek near Blum is a reddish clay 19 feet thick. With the advent of 

 the clay facies the shell conglomerates of the northern section disappear 

 and a pyrite fauna similar to that of the Duck Creek marl appears. This 

 little investigated fauna contains Area sp., and other small pyritic and 

 limonitic pelecypods and gastropods. 



DUCK CREEK MARL FAUNA 



This fauna is notable for its large number 'of small pyritic and limo- 

 nitic gastropods and pelecypods. Such genera as Cerithium, Cinulia, 

 Turritella, Turbo, Lunatia, Area, Nucula and Corbula are highly char- 

 acteristic of the lower Washita pyrite zones. Equally characteristic if 



