26 James E. Conkin, Barbara M. Conkin, William T. Mason, Jr. 



The stratigraphic position of the lower gravel and sand unit within 

 the Pleistocene sequence could not be determined. 



Introduction 



Little work has been done on Pleistocene molluscan faunas in south 

 Texas. Measured sections with stratigraphic placement of faunas have 

 been presented only by Conkin and Conkin ( 1962 ) . Sellards ( 1940 ) , 

 in his work on the Pleistocene Berclair terrace, dealt primarily with the 

 vertebrate fauna and artifacts, while the snails reported by him were 

 merely listed and not precisely placed within the Pleistocene sequence. 



This paper is a continuation of detailed stratigraphic placement of 

 molluscan faunas within the Pleistocene sequence of Texas. The field 

 work for this study was completed in 1955. Sections were measured 

 by hand level and rod. 



Acknowledgements 



The writers are grateful to the following individuals who were 

 helpful during the completion of this paper: Dr. Joseph P. E. Morri- 

 son, Associate Curator, Division of Mollusks of the United States Na- 

 tional Museum, for identification of several species and for supplying 

 U. S. National Museum pleisiotype numbers; Mr. Robert Gunn of the 

 Botany Department of Iowa State University at Ames, Iowa for tenta- 

 tive identification of the sedge seed, Scleria? sp. 



Stratigraphy 



The Pleistocene deposits in the Fordyce Quarry at San Patricio, 

 County, Texas (Text-figure 1) are herein divided into two units. 



The lower unit, a sand and gravel conglomerate, contains much 

 chalcedony, chert, petrified wood, quartz sand and pebbles, and small 

 vertebrate fragments, including bones and teeth of Equus cf. E. com- 

 plicatus. Reworked and silicified specimens of the Devonian tetra- 

 coral Heliophyllum, and Cretaceous Foraminifera in chert were found 

 in the gravels (Conkin and Conkin, 1962, p. 345); however, most of 

 the sediments were derived from younger beds as evidenced by re- 

 worked Tertiary and Quaternary horse teeth and fragments of silici- 

 fied Miocene palm wood. A portion of the gravel may be derived from 

 erosion of gravels of the Pliocene Goliad formation. No mollusks were 

 found in the lower unit. This lower unit cannot be precisely placed 

 stratigraphically within the Pleistocene sequence. 



The lower unit is unconformably overlain by an upper unit con- 

 sisting of silt and subordinate amounts of coarse to medium-grained 

 sand, with humus in the upper few feet. Caliche is disseminated, or 



