The natural geologic features seen along the Ice Age Trail help us to understand the history of glacial retreat, or deglaciation, in coastal Maine. There is a zone that extends inland about 25 miles from the coast in which there are hundreds of moraine ridges formed along the glacier margin. The moraines show crosscutting patterns in some places, revealing that the margin retreated inland across the coastal zone in an uneven manner. It often paused in one place for a time or briefly pushed forward during its overall northward recession.

Expansions and contractions of continental ice sheets have resulted in complex interactions of land and sea. Worldwide sea level was lower than today during the Ice Age because so much water was tied up in glaciers. However, the great weight of the ice sheet pushed the land so far downward that the sea flooded low areas of southern Maine and lapped against the southern edge of the ice as it retreated. Coastal Maine, especially along the Ice Age Trail, is the best area in the United States to see well-developed glacial features formed where the ice met the sea. These landforms have been exposed to view by coastal erosion, agricultural clearing of the land and excavations in gravel pits.

Great quantities of sand and gravel washed into the sea and accumulated as deltas along the ice margin. Low-lying areas of coastal and central Maine were covered with a blanket of marine mud that washed out of the glacier and settled to the ocean floor. Fossils in these sediments date to between 17,500–13,300 years ago. The species of fossil marine shells reveal that this early sea was colder than today and similar to modern Arctic regions.

As the glacier covering southern Maine thinned and the margin retreated northward, the removal of the heavy ice load soon caused the land to rise. Worldwide sea level has likewise risen during postglacial time because ice has melted and returned water to the sea. This process probably accounts for the many flood stories recorded in the histories of past and present human cultures. However, the land in Maine rose so much and so quickly that the formerly drowned coastal region emerged within a few thousand years. Thus, we experienced a falling relative sea level, marked by the position of Maine’s shoreline, despite the rise in worldwide sea level. Deltas and beaches that mark former sea level along the Ice Age Trail were uplifted as much as 250 feet above today’s ocean shore.

In eastern coastal Maine, the retreat of the glacier halted for a time as the margin stabilized, thickened and pushed forward along a line extending from at least Cherryfield east through Lubec and into coastal New Brunswick. Along this 100-mile front, the Pineo Ridge Moraine System marks the limit of the readvance. The Pineo Ridge Moraine System is composed of very large and closely spaced moraines along with ice-contact marine deltas, such as the Pineo Ridge and Columbia Deltas. This robust moraine system locally crosscuts earlier moraines to the south. North of the Pineo Ridge Moraine System, there are fewer moraines, but there are great volumes of glacial sand and gravel that washed out of melting glacial ice. These deposits include gravelly esker ridges formed in ice tunnels, some of which extend from the Pineo Ridge Moraine System northward for 50 to 100 miles.

To read more about Maine in the Ice Age, check out these more indepth explanations: Eskers and Deltas, Marine Clay, Salt Marshes and Recent Sea Level Rise, Moraines, Chronology, Abrupt Climate Change