The Geology of Mount Desert Island

A Visitor's Guide to the Geology of Acadia National Park


Having seen the effects of glacial ice and modern processes on Mount Desert Island, our geological overview of the region is now complete. The geologic history of Mount Desert Island is a long one; rocks over 500 million years old present evidence for the island's beginnings on the bottom of an ancient ocean floor. "Younger" rocks, approximately 400 million years old, show that the island was once the site of volcanic activity. A large part of the geologic history is unknown - no geologic evidence is present for the period from 350 million years ago until late-glacial time (approximately 15,000 years ago).

A wide variety of geologic processes have affected the island in the past: deep burial and metamorphism at high temperatures and pressures altered sediments to form the Ellsworth Schist; magma rose and intruded the sedimentary and volcanic rocks to form the granites that make up the core of the island; thick ice sheets sculpted the bedrock and pushed the land below the sea. Geologic processes, principally erosion, continue to alter the island's form today.

These processes affected more than just the island's landscape. Granite quarrying was a major industry on Mount Desert Island and continues to play a small role in the economy of the greater Penobscot Bay region. The good harbors sculpted by ice provide shelter for the region's fishermen and boating enthusiasts. And today, the spectacular scenery of Acadia National Park is the largest economic factor in the area.

We hope that this description of the area's geology has contributed to your understanding of the events that shaped this scenic part of the Maine coast, and that you can use this information to enrich your travels on the island. If you wish to study the development of the island's landscapes in more detail, you should consult the publications mentioned in the supplementary reading list at the end of this bulletin.

For anyone contemplating an extended tour of Mount Desert Island, a large topographic map, "Acadia National Park and Vicinity, Hancock County, Maine," is most useful. This may be obtained at the Acadia National Park Visitor Center and in local book and outdoor supply stores. Topographic quadrangle maps of the Mount Desert Island area are available from the latter sources, as well.

More casual visitors can obtain a copy of the map of Acadia National Park from the Visitor Center, Thompson Island Information, or Nature Center. Trail maps of Mount Desert Island are also available from the Park information centers and in local book and outdoor supply stores.

Introduction   Bedrock   Stratified Rocks   Igneous Rocks   Structure   Schoodic   Isle au Haut   Bedrock History   Glacial   Erosion   Retreat   Glacial History   Processes   Conclusion   Reading   Glossary   Maps

Last updated on 11 January, 2008