Cardinal Brook Intrusive Suite is here named in the cores of the Chester-Athens dome and Rayponda-Sadawga dome in the eastern and southern Green Mountains, VT, and the northern part of the Berkshire massif, MA. Includes the Harriman Reservoir Granite (new name) in the eastern half of the Rayponda-Sadawga dome, VT., the Stamford Granite of Hitchcock (1861), the Somerset Reservoir Granite (new name), and the Bull Hill Gneiss of Richardson (1931). Harriman Reservoir Granite consists of post-tectonic megacrystic, mylonitic biotite granite gneiss that intrudes Middle Proterozoic gneiss of the Mount Holly Complex. Overlies Middle Proterozoic basement; unconformably underlies Hoosac Formation and younger units. Previously mapped as Bull Hill-like gneiss within the Wilmington Gneiss. Age is Middle Proterozoic based on a U-Pb zircon age of 960-950 Ma.

Source: GNU records (USGS DDS-6; Reston GNULEX).