During portions of the past two field seasons the writer has been engaged in the areal mapping of the Theresa and Alexandria Bay quadrangles in northwestern New York (Jefferson county). While the main problem was the investigation of the pre-Cambrian rocks, the importance of a careful study of the Paleozoic series was fully appreciated, since this is the region of the Frontenac axis, and since little work has been done on these rocks since Emmons studied them, seventy years ago.
Work was begun about Theresa, where the pre-Cambrian rocks and the overlying Potsdam sandstone were studied and mapped. Above the Potsdam a series of somewhat calcareous, sandy dolomites with inter bedded weak sandstones was found—a series which is lithologically precisely like beds which, in the region farther east, lie between the Potsdam and Beekmantown formations and have always been regarded as “passage beds” between these, two formations. The work . . .