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Smith (1907) regarded the Ellsworth formation of folded, argillaceous schists and gneisses in the Penobscot Bay region, Maine (Fig. 1) as older than the Castine formation of acid flows and pyroclastics. This relation was based upon the degree of crumpling and shearing in the two formations and upon the intrusion of volcanic dikes into the schists. These dikes, however, have not been proved Castine equivalent. As Smith states, "the relations are not very clearly shown." Previously unmentioned are the recrystallized flows and pyroclastics which are interbedded in the upper part of the existing Ellsworth schists and gneisses. These volcanics have undergone recrystallization to form metaandesites and metatuffs. Smith elected to call this portion of the Ellsworth, Castine. Stewart (1946) found the same rocks on Deer Isle formerly mapped as Castine to be Islesboro equivalent, which is probably Ellsworth equivalent. The Ellsworth formation striking generally N 50-60' E was folded and metamorphosed, presumably during the Taconic disturbance. Regional metamorphism recrystallized the Ellsworth pelites, impure arennites, pyroclastics, and flows to chlorite-biotite schists, quartzites, and metaandesites and tuffs. Later thermal metamorphism by granitic intrusions further recrystallized these rocks into hornfels, feldspathic gneisses, cordierite-andalusite-anthophyllite gneisses and schists, biotite schists, and quartizites near the Ellsworth-granite contacts. Post-middle Silurian movements in this area folded but only weakly and locally recrystallized the rocks as attested by the Ames Knob formation, which crops out on North Haven Island 17 miles south. Here folded but unmetamorphosed limestones contain well preserved Niagrian fossils. The folded Castine trending N 10-300 E locally displays a slaty cleavage, which cannot possibly be mistaken for the high degree of Ellsworth recrystallization. The broad folds of the Castine and Ames Knob formations are probably related to Middle Silurian folding as Bastin (1914) found in the Eastport, Maine area. The Castine formation consists of very weakly metamorphosed, folded felsites, rhyolites, blue and green andesites, pyroclastics, and sheared |
