Islesboro Formation is of Late Proterozoic age. Consists of interbedded pelite, siltstone and sandstone, limestone and dolomite, conglomerate, rhyolite, and basalt. D.B. Stewart (1990, oral commun.) considers Islesboro to be distal facies of North Haven Greenstone, Ellsworth Schist and schist at Columbia Falls (eastern coastal ME).
Source: GNU records (USGS DDS-6; Reston GNULEX).
Age of Islesboro Formation changed to Late Proterozoic(?) and Ordovician(?). Some carbonate rocks previously designated as Coombs Limestone Member are reassigned to Seven Hundred Acre Island Formation (new name). Because the carbonate sequences within Islesboro Formation have different stratigraphic positions, variable thickness and lithology along strike, and may resemble each other locally, continued regional use of the name Coombs Limestone Member is unwarranted.
Source: GNU records (USGS DDS-6; Reston GNULEX).
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