Early Ludlow Graptolites from the Presque Isle Quadrangle, Maine

Seven graptolite assemblages collected from the upper member of the Perham Formation in the northern part of the Presque Isle quadrangle, Maine include fourteen species of monograptids which are described. The assemblages indicate an Early Ludlow age for the beds bearing them because they are closely similar to those typifying the lower part of the Ludlow Series in its typical exposures in Wales. The association of species described herein from the Presque Isle quadrangle is similar to that of the M. nilssoni and M. scanicus zones of the British Silurian graptolite succession. The M. nilssoni and M. scanicus zones can not be validly distinguished in Britain and they have not been recognized as separate zones elsewhere. The strata of the M. nilssoni and M. scanicus zones in Britain are concluded to be characterized by but one zonal congregation of species and thus to comprise but one zone and not two. The Presque Isle collections indicate that the beds bearing them are correlative with an M. nilssoni zone in this expanded sense. The beds bearing them are also correlated with the M. nilssoni and M. bohemicus zones of the Cape Phillips Formation in the Canadian Arctic.