This image is a homage to my hometown. As a child, I explored the Green Mountains with curiosity—wondering what lay beneath the soil, how these mountains formed, and why a ridge rises in one place while a valley settles in another. Decades later, I returned in search of deeper answers. This image reveals approximately 4¼ miles of depth below Shrewsbury in central Vermont, looking north–northeast.
The darker metamorphic rock that dominates the image is gneiss forming the core of the Green Mountains—the ancient block of crust geologists refer to as the Green Mountain massif. These rocks originated roughly 1.4 to 1.3 billion years ago during the Grenville Orogeny, an early mountain-building event that long predates the Appalachian Mountains. That immense range gradually eroded, and the Iapetus Ocean opened along the eastern margin of North America.
The lighter dolostone and quartzite layers visible along the lower and left portions of the image were originally deposited as marine sediments within that ocean basin. As the ocean began to close, these sediments were compressed, uplifted, and folded during the Taconic Orogeny between approximately 500 and 440 million years ago.
Large slices of crust were thrust westward, placing older Grenville-age rocks atop younger marine sediments as tectonic plates converged. The Iapetus Ocean ultimately disappeared as continents assembled into the supercontinent Pangaea. When Pangaea later broke apart, the Atlantic Ocean opened and extensional forces fractured the crust along eastern North America.
The vertical igneous conduit on the right side of the image—the Cuttingsville Stock—formed roughly 100 million years ago, when magma rose through fractures in the Green Mountain rock and solidified as syenite and essexite.