NPS photo

Bubble Rock, a glacial erratic

While the term "geologic formation" often conjures images of the spectacular arches and pinnacles of the western parks, many of Acadia's geologic features are subtle, but equally as impressive.

Just as the sedimentary rock of the Grand Canyon was carved by the effects of millions of years of water and wind, ridges of granite were sculpted by glaciers measuring up to 9,000 feet thick, creating the landscape of Acadia that we see today. Evidence of the glaciers can be seen just about everywhere: broad U-shaped valleys hold lakes, glacial erratics dot the landscape, as do glacial erosional scars like chatter marks, striations, glacial polish, potholes, and kettle ponds. Perhaps the most obvious reminder of Acadia's glacial legacy is the fjord-like Somes Sound (the only feature of its kind on the U.S. Atlantic Coast) with its deeply carved head and shallow mouth of glacial deposits.

Several other interesting geological features were formed when the sea level rose as the glacier melted, flooding today's coastline to a depth of about 250 feet. The earth's crust, freed of its burden of ice, started to rebound. Terrestrial deposits of marine clays, raised shorelines like the cave on the Cadillac Cliffs Trail of Gorham Mountain, and raised cobblestone beaches are all examples of the effects of this glacially caused depression and rebound.