Surface Geologic Map of Maine
Image adapted from Maine Geological Survey (fair use policy)
The surface of Maine is largely covered not with bedrock, but with sand and gravel and clay from the Ice Ages of Pleistocene time, starting about 1.6 million years ago. Enormous continental glaciers slowly bore down from the Canadian Shield several times, each time covering the region thousands of meters deep in ice. The weight of the ice depressed the crust by as much as 150 meters. And because so much water was frozen into ice, the sea level was much lower than today.
Glaciers scrape up huge amounts of sediment as they move, carrying it toward their toes. There the sediment is piled up into long heaps called moraines. And when glaciers melt, the sediment they're carrying drops straight down in a mixed form called till. That's what covers the great majority of Maine, shown in light green. The moraines are largely gone because the sea has covered them. In fact, the meltwater filled the sea faster than the depressed land could rebound, and as a result a large fraction of Maine was under the ocean just 10,000 years ago. That's where the dark blue glaciomarine deposits come from.
Another notable glacial legacy in Maine is an abundance of eskers. These are narrow, winding mounds of sand that were built underneath the glaciers where rivers of meltwater flowed. Some are as level as roadbeds, and many have been quarried for their sand. In the low, swampy land of much of Maine's interior, eskers can be an important ecological niche.
More Maine resources on About.com:
Maine Travel
Maine Maps
Maine Geography, State Symbols & Facts
Maine Campgrounds
Maine National Parks
Maine Scenic Roads
Maine Bed & Breakfasts
Maine Fishing
Maine Archaeology
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