Dolomite containing crystal molds of gypsum is present in Salina (Upper Silurian) rocks of northern Ohio. Similar molds have been reported from rocks of other ages. The layers containing the gypsum molds are unfossiliferous but stromatolites are common in associated layers. Penecontemporaneous gypsum and dolomite are known in recent sediments. Associated fossils and sedimentary structural evidence indicates that the molds may be used as markers for a penesaline environment of deposition.