Guide to the Cultural and Natural History of the Four Soldiers Path

Randolph's Geologic Foundation

Walking along the path, you’ll see loose boulders and rocks that are
vestiges of the last glacier to cover the region.

Underneath the Four Soldiers Path lies bedrock that differs from anything you would find just across Route 2, in the “big hills” of the Presidentials. All the RMC paths on or adjacent to the Crescent Range run across what are known as Oliverian Domes, made of 450,000,000-year-old igneous rock. Igneous rock, one of the three basic classifications of rock, along with sedimentary and metamorphic, comes pretty much straight from volcanoes. The rock itself in these domes is pinkish to light colored and granite-like with dark mica or biotite, quartz, and feldspar.

The Oliverian Domes were once magma chambers in a chain of volcanic islands in an ancient ocean called the Iapetus, an early version of the North Atlantic. As continental plates moved, the ocean closed, and the volcanics and frozen magma stuck to what is now the east coast of North America. After this collision, the frozen granitic rocks of the domes had a lower density than the basaltic volcanics that overlay them. As a result, the solid granitic rocks actually floated and flowed up and through the volcanics. The volcanic rocks, called the Ammonoosuc volcanics, can be found on the south side of Route 2.

The bedrock geology changes subtly when the path gets to within about one half of a mile of the Pond of Safety. Here is found a similar looking granitic rock called syenite. It is different only by the presence of a mineral called hornblende, and no, or very little, quartz. The rock is still pinkish in color, Ordovician in age, and part of the magma associated with the old volcanoes described above.

Regardless of the origin of the bedrock, it has been weathered, broken apart by freezing and melting water in cracks, and ground into loose boulders and small rocks by several huge continental glaciers over the past 100,000 years. The last glacier to cover the region, which receded about 12,000 years ago, left a blanket of rubble called glacial till. This is what makes up rocky landscape you can see in places along the path where it isn’t covered by soil and vegetation.

Note: The Oliverian dome rocks are exposed in stream beds and on Lookout Ledge, especially, as well as along the Four Soldiers Path in the cut areas nearest town where erosion has exposed them. Here, too, can be found an occasional glacial erratic, rocks from the north, deposited by the glacier. For example, look for a one-foot-diameter layered rock right in the middle of the trail, next to a trail blaze on the left side of the trail heading up, and on an old skid path in the area mentioned above. Its striped layers are different types of rock in contact with each other.

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