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Marlboro Beach, Lamoine, Maine
Marlboro Beach in the town of Lamoine has an interesting sequence of exposures of glacial and glacial marine deposits, as well as bedrock outcrops, best seen along the shoreline at low tide. To get there, follow Route 1 east from Ellsworth, bear right on Route 184, turn left onto Route 204 and right on Raccoon Cove Road to the boat launch. A stroll along the beach from the Town Boat Launch site to Old Point at the eastern end of the beach provides an opportunity to view several different geological features (Location Map).
One can access the western end of the beach from the boat launch area . There, one can see an erosional bluff exposure (Figure 2); photos also show change of summer and winter seasonal beach composition (Figure 2, Figure 3). Erosion and slumping of the bluff brings vegetation down (Figure 4, Figure 5).
The eroded bluff shows sandy stratified glacial marine deposits overlying glacial marine clay (Figure 6, Figure 7, Figure 8). The clay was deposited into the ocean during the end of the last ice age. As the glacier melted away from the region, the land began to rise due to the loss of the ice mass. As the land rose, it eventually came through the ocean surface and currents there winnowed the glacial deposits leaving the sandy deposits as a relict shoreline.
Continuing along the modern shore, you will encounter an outcrop of bedrock that has several interesting aspects. The outcrop is made up of two different rock types, where one rock type cuts across the other (Figure 9). Here in Lamoine, the most common local bedrock belongs to a unit called the Ellsworth Schist (or Ellsworth Formation). The darker rock cutting the Ellsworth Schist is an intrusive dike that formed later than the Ellsworth Schist. There are other features found on this outcrop that are related to the last glacial period. When the great ice sheet was here, streams issued from drainage channels within and beneath the ice. These streams, especially those that flowed beneath the ice, may have been laden with sediment. One can see features on the outcrop that look like they were sculpted into the rock surface; the shovel handle in the photo (Figure 9) is lying against the rock surface where the sculpted features can be seen. A closer look from a different perspective (Figure 10) shows what appear to be a series of cuspate surfaces. Some geologists interpret these cuspate erosional surfaces to be the product of water charged with sediment flowing under great hydraulic pressure over the bedrock beneath the ice and carving these features into the rock surface.
The final part of the walk along the beach brings us to a large outcrop of the Ellsworth Schist. The view in Figure 11 is toward Old Point taken from Meadow Point across Raccoon Cove; the island in the foreground is Shooting Ledge (see below for more information on this feature). From a distance, the author first thought the gray bluff was glacial marine clay. This rock exposure is quite steep and it should not be climbed, although exposure at the base of the outcrop may be examined (Figure 12). Beyond the large bedrock slope, flat bedrock surfaces that have glacial grooves and striations that range from 130 to 137 degrees may be seen (Figure 13, Figure 14).
The ledge exposure named Shooting Ledge at the entrance to Raccoon Cove piqued the interest of the author; why Shooting Ledge? The first thought offered by a colleague was that it might be a smaller feature like Thunder Hole in Acadia National Park, where incoming waves crash into a crevice in the bedrock coast and forces the air and water to shoot up into the air intermittently. Geological terms for these features include spouting horn, blow-hole, blowing cave, spouter, and puffing hole. A second guess was whether it had been used for target practice by the military (MGS Field Locality: Reid State Park). A call to the Lamoine Town Office inquiring about the Shooting Ledge added to the mysterious name when the author was told that it is also known as Shooter's Ledge, so-called because it was where the duck hunters would set up blinds and shoot ducks as they flew in toward the cove. There was no knowledge of it ever having been an area for military target practice, or that there is a spouting horn there.
For More Information
Reusch, Douglas N., 2003, Bedrock geology of the mainland portion of the Newbury Neck and Salsbury Cove 7.5-minute quadrangles: Maine Geological Survey, Open-File Report 03-92, 14 p. report, 22 figs (1.6 Mb pdf format).
Weddle, Thomas K., 2012, Surficial geology of the Salsbury Cove quadrangle, Maine: Maine Geological Survey, Open-File Map 12-8, scale 1:24,000 (2.0 Mb pdf format).
Text and photos by Thomas K. Weddle.
Originally published on the web as the January 2013 Site of the Month.
Last updated on February 6, 2013
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