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Web Extras for Chapter 5: Metamorphic Rocks
7.
Exploring the geology of Acadia National Park (Maine). Now that you know the basics of the three major
rock groups, you can investigate the geology of a given state or national park before you visit. The quality of
information available for individual parks varies widely, but it so happens that the Maine Geological Survey has
posted a number of excellent guides to park geology. Visit www.mine.gov/doc/nrimc/mgs/explore/bedrock/ and
click on The Geology of Mount Desert Island, which comprises most of Acadia National Park.
a.
Click on the Bedrock Geology of Mount Desert Island (2.5 Mb PDF file) link to get a geologic map of the
island. This map shows you the type of rocks that you will find either exposed at the surface or under a
thin covering of loose soil or sediment anywhere on the island.
Along the right side is a map explanation that describes each of the rock units (youngest at the top to oldest
at the bottom), the map symbols, and several specific sites of interest. Note that each different body of rock
has a different name and a three-letter code and specific color to mark its locations on the map.
Examine the map and look for the presence of map units with the letter ‘g’ in their code (e.g., Dgd, Dcg,
Dsg, Dsg1, etc.). The ‘D’ stands for a period of geologic time called the Devonian, ‘g’ stands for one of
two rock types, and the remaining letter often refers to the name of the formation (e.g., ‘c’ stands for
Cadillac).
(1) According to the Explanation, what type(s) of rock does the ‘g’ stand for?
(2) Are the ‘g’ units a minor part of the island, or do they dominate much of the park?
(3) Did these ‘g’ units form on the surface or deep underground?
b.
Read the description in the Explanation of the oldest rock unit, the Ellworth Schist.
(1) What three minerals does this schist contain?
(2) Of these three minerals, which is the best index mineral? What metamorphic grade does it indicate for
the Ellworth Schist (see Fig. 5.12)?
(3) Where on the island do you find the Ellworth Schist?
c.
Now return to the website and click on the Bedrock link in the upper left corner. Click on Stratified rocks in
the upper left corner to learn more about the Ellsworth Schist. What was the parent rock of the Ellsworth
Schist?
Web Extras for the Laboratory Manual for Physical Geology by Jones and Jones (McGraw-Hill).
d.
Read about the lowermost member of the Cranberry Island Series (unit SDcis) in the map’s explanation.
(1) What type of metamorphism is described?
(2) Which metamorphic rocks were produced?
(3) Describe any evidence for directed pressure during this metamorphism.
e.
Given the abundant igneous intrusions and evidence for directed pressure, what type of tectonic boundary was
present along the Maine coast (e.g., ocean-continent convergent, continent-continent convergent, ocean-ocean
divergent, continent-continent divergent, transform, etc.)?
f.
Look at the map of the Earth’s tectonic places inside the front cover of your lab manual. Is a plate boundary
still located along the coast of Maine?
g.
If you like, continue reading the materials posted on this website to learn more about the park. In general, you
will find that if you know something about the geology of the park, you will pay more attention to the rocks and
find more interesting things to think about during your visit. Understanding geology definitely makes the world
a more interesting place!
Web Extras for the Laboratory Manual for Physical Geology by Jones and Jones (McGraw-Hill).