New Bedrock Geologic Map Released
The Maine Geological Survey (MGS) is pleased to announce the release of a new bedrock map, Bedrock Geology of the Cumberland Center Quadrangle, Maine, which covers a rectangular area north of Portland in Cumberland County. Surprisingly, it is the first detailed bedrock map of this area at 1:24,000 scale, greatly improving the resolution over the previous 20-year-old regional map at 1:100,000 scale.
 The bedrock is dominated by two mapped formations of Silurian metamorphic rock (deposited approximately 420 to 430 million years ago), intruded by a variety of younger granites and granitic pegmatites, probably Devonian to Permian in age. (Granitic rocks in the surrounding area are ~360 to 298 million years old.) In contrast with rocks nearby to the southeast in Falmouth, the rocks in the central part of the map area are at high metamorphic grade, including partially melted rocks (migmatite) and gneisses in addition to the abundant granites.
 Photo: Large black tourmaline crystals in a pegmatitic patch within fine-grained granite from the southern part of the Cumberland Center quadrangle.
This map draws heavily on previously unpublished mapping by Matthew Engelman, who did extensive field work for an undergraduate thesis while a student at Bates College under the supervision of the late Professor John Creasy, an authority on igneous rocks of southern Maine. This map is part of a larger effort by MGS to improve the quality of bedrock maps in the area between Portland and Lewiston, with recent publication of maps in the Yarmouth, North Pownal, Lisbon Falls North and South, Monmouth, and Lewiston quadrangles. Mapping is ongoing in other parts of the state as well. All modern bedrock maps are produced in GIS supported by relational databases which greatly expands the accessibility of data for multiple uses.
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