Cave Hill Geology

Cave Hill Conservation Area and Trails

Geology of the Cave Hill Conservation Area

Geological Era Map-with-layers c web

The eastern section of the Cave Hill Conservation Area is part of the Gander Terrane, which is a microcontinent that at one time was located north of Africa. The Poplar Mountain Gneiss and the Dry Hill Gneiss both formed about 600 million years ago on the Gander Terrane. The Gander Terrane collided with North America around 430 million years ago.


The western part of the Cave Hill Conservation Area has rocks that were never a part of the Gander Terrane, but rather formed here on North America. These volcanic and sedimentary rocks were deeply buried and deformed around 380 million years ago when yet another continental collision added to North America the rocks upon which Boston is now built.These rocks belong to the Ordovician (about 450 million-year-old) Four-Mile Gneiss and Partridge Formations, and to the Devonian (about 410 million-year-old) Erving Formation.

The boundary between the eastern and western parts of the property is part of the boundary between these two blocks that make up part of the North American continent. The fact that a continental suture is exposed within this area makes it a hugely valuable site for study by local geologists and geology students.

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