Name Orrs Mills Member of Rondout Formation is here proposed for strata overlying the Clove Brook Member of the Decker Formation and underlying the Duttonville and Whiteport Members of the Rondout at Cornwall, New York. Rocks were included in the upper part of the Decker Ferry Formation by Kummel and Weller (1902) and called Cobleskill and Decker Ferry Limestones by Hartnagel (1907). Lower two-thirds of the Orrs Mills is composed of olive gray to brown slightly dolomitic and calcareous shale. Upper third is medium-dark gray argillaceous sublithographic dolomite and dolomitic shale. Poorly developed slaty cleavage. Upper third contains abundant coral and is correlative with the biostromal limestone of the Decker Formation at Nearpass Quarry. Unit is present exclusively in the Green Pond-Schunemunk Mountain outlier of southeastern NY. Laterally replaces that portion of the Clove Brook Member of the Decker Formation above the hematitic marker. Only known occurrence is near Cornwall where thickness is probably 25 to 27 ft. Age is Late Silurian and Early Devonian (Cayugan and Helderbergian). [First use as member of Decker Ferry Formation (Barnett, 1967: Dissert Abs., v. 27, no. 9, sec. B, p. 314)]

Source: GNU records (USGS DDS-6; Reston GNULEX).