"The Revett-St. Regis transition zone is a 100 to 150 m thick sequence of fine-grained sediments deposited in a Precambrian basin in northwestern Montana and northeastern Idaho. The Revett-St. Regis transition zone represents a gradual, upward fining sequence from well-sorted quartzites in the Revett Formation to siltites and argillites of the St. Regis Formation. Although both formations thin to the northeast, the Revett quartzites pinch out completely and St. Regis lithology directly overlaps the Burke Formation normally located beneath the Revett. In the Revett Formation there is a unique association of parallel laminae showing heavy mineral zoning, multidirectional medium-scale cross-bedding, symmetrical wave ripples, truncated wave-ripple laminae, and lenticular geometry of quartzites. This association indicates the Revett was probably deposited in a nearshore beach, and possibly barrier island, environment. The Revett quartzites interfinger vertically with and gradually give way to siltites and argillites of the St. Regis Formation. Associ-ation of wavy and lenticular sand-mud laminae, mud cracks, mud chips, burrow-like structures, interference ripples, and small channels in the St. Regis indicates it was probably deposited under tidal and supratidal conditions. Hrabar (1971) suggests that the Revett-St. Regis Formations were produced by turbidites during a flysch phase of sedimentation. Detailed study of parallel lamination and straight-crested, symmetrical ripples in the Revett and mud cracks in the St. Regis show that Revett-St. Regis rocks were definately deposited above wave base. I believe the Revett- St. Regis rocks were deposited in water ranging in depth from wave base for parts of the lower and middle Revett up to water a few centimeters deep for parts of the upper Revett and most of the St. Regis Formation. The unique association of sedimentary structures and lateral and vertical characteristics observed in rocks of the Revett and St. Regis Formations indicate they probably represent an ancient shallow water shore face, beach barrier bar, and supratidal-tidal flat complex. This complex was formed during a regressive cycle and a subsequent shallow transgressive cycle"--Document.