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Scientific Investigations Map 3052

Prepared in cooperation with the
State of Connecticut, Department of Environmental Protection,
Geological and Natural History Survey

Bedrock Geologic Map of the Old Lyme Quadrangle, New London and Middlesex Counties, Connecticut

By Gregory J. Walsh, Robert B. Scott, John N. Aleinikoff, and Thomas R. Armstrong

Thumbnail of sheet 1 of SIM 3052 (3.05 MB) Thumbnail of sheet 2 of SIM 3052 (3.19 MB)


The bedrock geology of the Old Lyme quadrangle consists of Neoproterozoic and Permian gneisses and granites of the Gander and Avalon terranes, Silurian metasedimentary rocks of the Merrimack terrane, and Silurian to Devonian metasedimentary rocks of uncertain origin. The Avalon terrane rocks crop out within the Selden Neck block, and the Gander terrane rocks crop out within the Lyme dome. The Silurian to Devonian rocks crop out between these two massifs.

Previous mapping in the Old Lyme quadrangle includes the work by Lawrence Lundgren, Jr. Lundgren's work provides an excellent resource for rock descriptions and detailed modal analyses of rock units that will not be duplicated in this current report. New research that was not covered in detail by Lundgren is the focus of this report and includes (1) evaluation of the rocks in the core of the Lyme dome in an effort to subdivide units in this area; (2) structural analysis of foliations and folds in and around the Lyme dome; (3) geochronology of selected units within the Lyme dome; and (4) analysis of joints and the fracture properties of the rocks.

Posted November 2009

Version 1.0
(Supersedes USGS Open-File Report 2006–1296)

For additional information, please contact Gregory Walsh.

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Walsh, G.J., Scott, R.B., Aleinikoff, J.N., and Armstrong, T.R., 2009, Bedrock geologic map of the Old Lyme quadrangle, New London and Middlesex Counties, Connecticut: U.S. Geological Survey Scientific Investigations Map 3052, 2 sheets, scale 1:24,000, 25-p. text, available only online at (Supersedes USGS Open-File Report 2006–1296.)

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