Paul W. Westerfield Gerard Gonthier David T. Poynter Aaron L. Pugh 1998 The Sparta Sand and Memphis Sand form the second most productive aquifer in Arkansas. The Sparta Sand and Memphis Sand range in thick- ness from 0 to 900 feet, consisting of fine- to medium-grained sands interbedded with layers of silt, clay, shale, and minor amounts of lignite. Within the three areas of interest, the top surface of the Sparta Sand and Memphis Sand dips regionally east and southeast towards the axis of the Mississippi Embayment syncline and Desha Basin. Local variations in the top surface may be attributed to a combination of continued development of structural features, differential compaction, localized faulting, and erosion of the surface prior to subsequent inundation and deposition of younger sediments. application/pdf 10.3133/wri984002 en U.S. Dept. of the Interior, U.S. Geological Survey ; Branch of Information Services [distributor], Altitude of the top of the Sparta Sand and Memphis Sand in three areas of Arkansas reports