The Geology of Groton State Forest

by Robert A. Christman

C. Erosion removes much of the rock from the area.

GRANITE

D. During the ice age, continental glaciers move over the land and erosion by the ice forms Owlshead Mountain and the basin for Groton Pond.

ICE GRANITE

E. Present topography, exaggerated.

OWLSHEAD MOUNTAIN RICKER MILLS

Evidence that the granite was emplaced into the older rocks of the earth’s crust can be seen at certain locations outside of the State Forest. At Ricker Mills, for example, narrow bodies of granite can be seen cross cutting the older rocks. A fuller description of the geology at Ricker Mills is given in a later section of this report. Another type of evidence showing that the granite came into older rocks is found in the occurrence of fragments of older rock incorporated into the granite. These are called inclusions and represent broken pieces of older rock which were enveloped by the granite. Inclusions are like peach slices in jello in that the surrounding material solidified after they were dropped in. Inclusions were observed in rocks on top of Kettle and Jerry Lund Mountains.