The occurrence of Rusophycus along horizons within the High Falls Formation(Late Silurian) at six localities in northwestern New Jersey indicates that marine conditions may have intermittently invaded what has heretofore been interpreted as a fluvial (meandering stream) environment. It occurs as bilobed casts on the base of parallel-laminated and cross-laminated mostly fine to medium sandstones interbedded with fine to medium cross-stratified sandstone, siltstone and shale. At two localities, horizons containing Rusophycus are present in the upper portion of fining-upward redbed sequences. Cruziana infrequently occurs in association with Rusophycus . The trilobites that produced Rusophycus and subordinate Cruziana probably inhabited interdistributary bays of a high constructive elongate delta complex. The lithofacies within which Rusophycus and Cruziana occur are interpreted as overbank flood, crevasse splay, and crevasse channel or distributary channel deposits produced by sudden incursions of flood-generated sand-laden currents.