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BTChronostratigraphic Units
 .Phanerozoic
 ..Paleozoic
 ...lower Paleozoic
 ....Penobscot Formation
RTCambrian
 Ordovician
 Maine
SNS central Maine. Cambrian? Later was considered Ordovician. Above Battio Quartzite; below Rockland Formation or Bucksport Formation. Indexed with age as applicable. Added to Thesaurus in 1989.