Eighty-nine surface samples and 17 subsurface samples of shale from the Blaine Formation (Permian) in western Oklahoma were examined to determine the variation in percentage of quartz and mean size of quartz with distance from a known shoreline. Samples were fused using sodium bisulfate to release the quartz from the mass of clay minerals. The surface samples gave areally and statistically meaningful trends; subsurface samples did not do so because of sampling difficulties. The mean percentage of quartz in surface samples decreases from 47 percent at a distance of 60 km from shore (more precisely, the sand-mud line) to 11 percent at 270 km from shore (r = .70), a loss of 10 percent quartz with each 60 km increase in distance. Mean grain size decreases from 5.2phi at 60 km from shore to 6.9phi at 270 km from shore (r = .71). Extrapolation of the data indicates that at the sand-mud boundary the percentage of quartz is 57 percent and the mean size of the quartz is between 4.75phi and 5.1phi . The percentage of quartz in mudrocks can be a useful indicator of the position of the shoreline in ancient fine-grained epicontinental sea deposits.