Heavy mineral placer layers within channel sandstones of the Morrison Formation (western United States) have been shown to contain a very stable, accurate record of the Jurassic geomagnetic field. These laminae are composed almost entirely of hematite grains; in particular, they are largely the hematite pseudomorph of magnetite, martite. The laminae record the correct geomagnetic field direction during a period of rapid apparent polar wander, which suggests an early acquisition of the remanence. Several other remanence characteristics imply that the remanence is probably a detrital remanent magnetization (DRM): (1) there is large directional dispersion in one lamina which had been heavily burrowed by organisms (measurement of individual burrows shows that the burrowing disrupted and randomized the magnetization held in the martite grains), (2) directions of laminae that were deposited on sloping surfaces are significantly deflected from the directions of the flat-lying laminae, (3) more than 50% of the martite grains have high-temperature oxidation features, suggesting that they may have been martite at the time of deposition. These characteristics, in particular the burrowing disturbance, strongly suggest that the martite was deposited as martite and that the remanence is a DRM, as opposed to deposition of magnetite grains which were altered to hematite after deposition. Examination of recent weathering debris on igneous outcrops shows a substantial amount of martite on these outcrops. This observation provides further evidence in support of the idea that hematite, and in particular, martite, can be a deposited mineral in sedimentary rocks and thus can carry a DRM.