Otter Cliffs
About 0.3 Km
Legend
North
Route from Gorham parking lot to Otter Point Parking lot
After Gilman and Chapman, 1988
Description of Rocks/Minerals
Cadillac Granite: This coarse-grained granite can be found across much of the eastern half of MDI. It is gray or pink in color with pink, white and black crystals. Those crystals are feldspar, quartz and hornblende respectively (Gilman and Chapman, 1988). In areas directly on the ocean, rock may be black due to bacteria.
Mineral Composition
Quartz (White):
SiO2
Potasium Feldspar (Pink): KAlSi3O8
Biotite (Black):
K(Mg,Fe)3(AlSi3O10(F,OH)2
Bar Harbor Formation: This layered rock is typically dark grey but can have hints of lavender or tan (Gilman and Chapman, 1988). Parts bordering granite may be darker and harder in what is known as a baked contact, resulting from the hot magma from which the granite formed heating the rock.
Page Written and Designed by Alison Bligh
Basalt Dike?! From a far distance, the gray Bar Harbor formation, eroded in blocks, may look like a basalt dike. However, one should see the layering of the meta-sedimentary rock upon closer inspection, which basalt does not have. Basalt is aphanitic (lacking visible grains), layerless and dark.
Timing of Events
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465 Million Years Ago: Sediment deposits on the ocean floor, creating the Bar Harbor Formation. (Braun and Braun, 2012)
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420 Million Years Ago: A massive magma chamber beneath a volcano hardens, creating the Cadillac granite (Braun and Braun, 2012). This magma bakes the Bar Harbor formation, creating baked contacts between the two rock types.
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Millennia of erosion and deposition occur that have been lost to time.
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15,000 Years Ago: Massive glaciers retreat, leaving behind scarred rocks and erratics
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Ongoing: massive waves and storms beat the cliffs, eroding them into their jagged forms, while also depositing large boulders.
Differential erosion (above). Baked contact between Bar Harbor formation and Cadillac Granite creating plane of weakness and eroding the Bar Harbor Formation at a faster rate.
(above) Massive waves and storms beat the cliffs, eroding them into their jagged forms, while also depositing large boulders.
(above) Wave erosion has created tide-pools along the fractures, providing sanctuary for intertidal life from the harsh seas.
(left) There are three fracture set averages orientating in different directions of 162, 077, 139. The three fractures sets intersect in some spots, creating a triangular tide pools.
Sometimes there's water here!
Directions
To get to Otter Cliffs, follow these instructions taken from Google Maps (2017).
References Cited:
Sources:
Braun, D. and Braun, R. 2012. Revised Mount Desert Island Bedrock Geology Map Explanation.
http://www.coa.edu/shall/Geoscience/Maps_and_Links_files/2012%20Revised%20MDI%20Units.pdf
Gilman, R.A. and Chapman, C.A. 1988. Bedrock Geology of Mount Desert Island. Maine Geological
Survey. Scale 1:50000