A specimen of the Perry Farm shale collected in Ray County, Missouri, was found to be a calcareous, micaceous sandy shale. Lamination is due to the essentially parallel orientation of platy minerals; micas, chlorite, illite, and kaolinite. Quartz, potash feldspar, and plagioclase with small amounts of tourmaline, zircon, rutile, and sphene comprise the major part of the sand-silt fraction. The coarse clay fraction contains sericite, chlorite, and kaolinite, whereas illite predominates (with a little montmorillonite) in the finer clay. Extensive laboratory evidence is given for the determination of the clay minerals. The marine origin of the shale is discussed in terms of its mineralogy.