The State of Maine has extensive information on the interesting rock geology of the state on their site. This link is a good overview and FAQ.

Stone Walls of Maine

The origins of New England’s wall stones date back to between about 30,000 and 15,000 years ago, when the Laurentide ice sheet made its way southward from central Canada and then began retreating.

40 million “man days” of labor would have been required to build the more than 380,000 kilometers of stone walls in New England.

Our home is located on the Bucksport Formation. Light gray, fine-grained to medium-grained, quartz-plagioclase-biotite granofels interlayered with greenish-gray, fine-grained, plagioclase-quartz-actinolite-diopside (calcsilicate) granofels. Layers generally range in thickness from 3 to 12 cm, but locally are as thick as 30 cm. Less common layers of rusty-weathering, medium-grained biotite schist are locally abundant. The unit is characterized by the distinct and sharp compositional layering of biotite granofels and calcsilicate granofels, which when weathered forms distinctive ribbed outcrop surfaces (Photo 6). Many outcrops contain sills, boudins, and less commonly dikes of granite or pegmatite giving these exposures an overall gneissic appearance (Photo 7). Locally, particularly near contact with the Cape Elizabeth Formation, very coarse grained, mottled green to pink, skarn-like calc-silicate rock containing grossularite and diopside is present. Additionally, several exposures (e.g., the southwestern tip of Dodge Point along the western side of the Damariscotta River, Newcastle) contain sills less than 20 meters wide of medium gray, plagioclase-hornblende-garnet gneiss interpreted to represent deformed and metamorphosed igneous rocks.