A layer of diatomaceous earth, 2 to 3 ft. thick, is reported in the Mullen Dam and Reservoir site, Hooker and Cherry counties, Nebraska. Impurities are 1% or less of quartz grains and black organic matter. Most of the diatoms are Naviculineae. A tentative identification of the snail Gyraulus labiatus indicates Yarmouth interglacial age.