The Second Pennsylvania Geological Survey reported “Tully” limestone but listed no characteristic fossils. So far as can be determined, none of their localities shows true Tully. Nevertheless, it is not impossible that that organization may actually have found the Tully, as all of their localities could not be rediscovered. The earliest record of the discovery in Pennsylvania of unquestioned Tully limestone with a diagnostic fossil (Chonetes aurora) appears to be that of Butts in 1918.1 Until 1934, this remained unique. In that year, and subsequently, the writer has reported the occurrence of Tully limestone and fossils in the State.2 These papers give an incomplete description of the Tully, because it had not been possible thoroughly to digest the data on hand at the time when these articles were prepared. The writer purposes now to present a fuller account of the Tully limestone and its fossils in Pennsylvania. . . .