USGS Visual Identifier
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Geologic Unit: Ammonoosuc

Ammonoosuc Volcanics (NH*,CT*,MA*,ME*,VT*)

Ordovician, Middle*
Ordovician, Late*

Geologic Province:
New England province*

Areal Extent:

Type Locality:
A district bounded on the north by Slate Ledge School and Partridge Lake, on the south by Youngs Pond (Ogontz Lake) and Tinkerville, Grafton Co., northern NH. Named from Ammonoosuc River (Billings, 1935).

Unit Name History:
Named (Billings, 1934).
Overview (Billings, 1935).
Areally extended (Hadley, 1949).
Age modified (Cady, 1960).
MA State Geol. Map usage (Zen and others, 1983).
Age modified (Moench and others, 1984).
Not used (Moench and Pankiwskyj, 1988).
Revised; Areal limits (Moench, 1990).
Age modified; Isotopic dating (Tucker and Robinson, 1990).
Age modified; Isotopic dating; Extended into ME; Revised (Moench and others, 1995).
NH State Geol. Map usage; Age modified; Isotopic dating (Lyons and others, 1997).

Note: If you need more information, please contact Nancy Stamm (
Asterisks (*) indicate usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" implies that a name has been abandoned or that it has fallen into disuse. Former usage and, if known, replacement name given in parentheses ().

Slashes (/) indicate unit name usage violates the 1983 North American Stratigraphic Code. This violation may be explained within brackets ([ ]).

U.S. Department of the Interior, U.S. Geological Survey, Reston, VA, USA
Database project personnel
Last modified: 15-Jan-2013