At Rattlesnake Butte, 23 mi. south of Interior, SD, the ridges are capped by coarse sandstone three to four feet thick containing: masses of prefect scalenohedrons, single crystals, radiating rosette structures, massive pipes, of sand calcite. The crystals were analysed by wet chemistry. Constituents separated by S.G. and studied with binocular and petrographic microscopes. Mineral species determined by R.I. Found: 37per thousand calcite; 0.2per thousand mud and silt; sand grains well rounded by wind action (ground surfaces) containing quartz, orthoclase, microcline, albite, muscovite, biotite, hornblend, augite, green- black- and colorless-prisms of tourmaline, zircon, garnet, staurolite, magnetite, and an opaque polished mineral possibly cassiterite.