The term “moraine” has been used in many ways. Current usage in the United States defines “ground moraine” as sediment deposited directly from a glacier. It is a random mixture of rock and mineral fragments ranging from clay to boulder size. This material is also called till, as shown on the Ice Age Trail map. It forms a discontinuous blanket on the landscape, and in low areas it commonly underlies younger sediments deposited from glacier meltwater.

“End moraines” (abbreviated to moraines on this map) are ridges of glacial sediment deposited along the margin of the ice. They can be composed of various sediments, including stratified sand and gravel deposited by meltwater coming off the ice, along with till released directly from the glacier. End moraines can accumulate when a glacier advances and bulldozes sediments into a ridge, or they may form when the forward flow of the ice is balanced by backward melting of the glacier margin. This allows the position of the margin to remain in one position for a while, during which sediments within the ice are conveyed to the margin and build a moraine.

Moraines in coastal Maine formed where the ice margin terminated in marine waters, as shown in the diagrammatic cross section. Often the coarse sediments coming from the ice became interlayered with mud settling out of the water from suspension. There are many places where the mud contains marine fossils, so we can be certain that it was deposited in the sea. This material is commonly known as marine clay, though in places it includes coarser silt and sand. The interfingering of the morainal deposits with the fossiliferous clay proves that the glacier margin was likewise in direct contact with the sea.

The orientations of the moraine axis record the trend of the glacier margin, which generally ranged from easterly to northeasterly in the area of the Ice Age Trail. Moraines farther inland are younger than those closer to the modern coast. In places where moraines are closely associated with fossil organic remains, the ages of the fossils can be measured by radiocarbon dating. These ages provide the basis for determining when the last glacial ice sheet retreated from coastal Maine.

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, Glacial Retreat, Chronology, Abrupt Climate Change