The Geology of Mount Desert Island

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

Otter Cliffs
Otter Cliffs at sunrise
by Robert M. Neff, copyright © 1986


Not only is Mount Desert Island one of the most scenic places on the entire Atlantic Coast, it is also one of the most interesting from a geologic point of view. This website will introduce you to the rock formations and glacial landscapes that record the more than 500 million years of earth history that went into the making of Mount Desert Island.

Maybe your imagination will be sparked by the fact that the location of the Acadia National Park Visitor Center was once part of a gigantic body of molten rock that cooled several miles below the surface of the earth, or that at another point in its history the same location was covered by hundreds of feet of glacial ice. And perhaps you'd find it intriguing to take a boat trip to the Cranberry Isles to see rocks that were spewed from volcanoes about 400 million years ago.

If these things interest you, read on; we will help you interpret the story that the landscape tells us. Part of this story is recorded in the bedrock exposed along the shore and on the mountain tops; other parts are recorded in the deposits of sand and gravel left by the glacier that once covered Maine's coast; and still other evidence is found in special features of the landscape that were carved by erosion over the past thousands of years.

The geologic history of the island can be conveniently divided into three parts: the period when the island's bedrock was deposited; the glacial period when many of the present day landforms were shaped; and the present day, when modern processes continue to modify the land. Two colored geologic maps (definition) of the island are associated with this guide. One, the bedrock geologic map (pdf format), shows the type and distribution of bedrock on the island as if all the overlying vegetation, soil, sand, and gravel were scraped off. The second, the surficial geologic map (pdf format), shows the type and distribution of materials deposited during and immediately after glaciation, as well as materials formed in recent times. These maps will be referred to frequently in the descriptions that follow.

Note: Italicized words are defined in the Glossary of Geologic Terms at the end of the text.

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 February 23, 2006