Provenance studies based on the mineralogy of sandstones seem to be falling rapidly into disrepute as a result of the increasing emphasis on the effects of diagenesis on the original detrital mineral composition. Feldspars in sandstones commonly are dissolved, altered to clay minerals, and albitized by widely occurring diagenetic processes. Accessory minerals all too frequently are confined in ancient sandstones to ZTR. Mudrocks, in contrast, have the potential of greater preservation of feldspars and accessory minerals because of their lesser permeabilities. Few studies have attempted to use the nonclay mineralogy of mudrocks for provenance work, and these few have had promising but mixed results. Mudrocks deserve more attention in provenance studies than they have received.