Roy and Mencher (this volume) presented an interesting summary of the stratigraphy of northeastern Maine. Counterparts to some of the lithotectonic units they described occur along strike to the south, although in detail the stratigraphy shows some marked differences. For comparative purposes, I will briefly discuss some of the similarities and differences in the stratigraphy on the west side of the Aroostook-Matapedia anticlinorium southward from the Presque Isle area.
The Carys Mills Formation (of Middle Ordovician to Early Silurian age) extends as a continuous unit throughout northeast Maine within the core of the Aroostook-Matapedia anticlinorium. The lithology and the internal stratigraphy of this formation have been described elsewhere (Pavlides, 1968Pavlides, 1966; Pavlides and others, 1965) and are essentially as described by Roy and Mencher (this volume) except for minor differences; for example, in the Bridgewater area, about 20 mi (32 km) southeast of Presque Isle, the formation contains lenses of slate and of slate and graywacke. Absence of marker beds hinders subdivision of the Carys Mills Formation into subunits, and Roy and Mencher’s subdivision of it into a lower and upper part north of Presque Isle is apparently biostratigraphic rather than lithostratigraphic.
The Frenchville Formation, of Llandovery C3 –C5 age, is absent along the west flank of the Aroostook-Matapedia anticlinorium; in the Mars Hill area (about 13 mi [20.8 km] southeast of Presque Isle), the coeval Spragueville Formation overlies the Carys Mills Formation and underlies the early Ludlow upper part of the Perham or Jemtland Formation of Roy and Mencher