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Great Falls Boat Launch, North Windham, Maine
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Two outcrops at this easily accessible location reveal some of Maine's ancient metamorphic rocks.
This EarthCache features two different outcrops of metamorphic rocks. Waypoints are provided for each outcrop, which are just a short distance from one another. Please visit both outcrops in order to complete this EarthCache.
Maine contains a good variety of metamorphic rocks. Metamorphic rocks are one of the three main categories of rocks, along with sedimentary rocks and igneous rocks. Metamorphic rocks are rocks that have been transformed physically and/or chemically a result of high levels of heat and pressure within the earth.
A metamorphic rock may start off as an igneous rock, a sedimentary rock, or even another metamorphic rock, before it is changed into its current state. The metamorphic rocks found here were originally sedimentary rocks. The original rocks formed from large quantities of sediments that were deposited during the Silurian Period (417-433 million years ago) in the Central Maine Basin, an ancient ocean basin situated at the eastern edge of early North America. The Central Maine Basin was part of the ancient Iapetus Ocean, which can be thought of as an earlier (pre-Pangaea) form of the Atlantic Ocean. Later, during the Devonian Period (354-417 million years ago), the Iapetus Ocean closed as a relatively large microcontinent called Avalonia collided with the early North American continent. This collision was one of the steps in the development of the supercontinent known as Pangaea. The collision caused the Acadian mountain building period, which marked the final stages in the development of the northern Ancestral Appalachian Mountains. The crust underwent major deformation, and sediments were buried more than 9 miles deep. The high levels of pressure and heat present at that depth transformed the rocks from sedimentary to metamorphic rocks. Further metamorphism occurred when the Sebago granite pluton intruded into the region during the Carboniferous Period (290-354 million years ago). The intense heat from this body of magma caused the rocks here to transform to an even higher "grade" of metamorphism, thus producing the rocks we see here today at this EarthCache.
There are two main rock outcrops at this EarthCache, and they are mostly composed of two main metamorphic rock types, schist and granofel.
In schist, most of the mineral grains are elongated, platy, scaly, or flaky. The mineral grains are aligned in such a way that it gives the rock a "foliated", or layered appearance. The direction, or trend of the foliation typically aligns 90 degrees from the direction of principal stress--the main direction from which the rocks received pressure. Mica, a shiny, platy, sometimes glitter-like mineral is often dominant. in Maine, the schists generally originate from mudstones.
A granofel is a metamorphic rock with medium to coarse-grained crystals, with a texture somewhat similar to granite, in that the mineral crystals show little elongation or alignment. Unlike schist, granofels are not typically foliated, but they may appear in layers due to their sedimentary origin as layers of sandstone.
This EarthCache lies very close to the contact between two major geological rock units. These units are called the Rindgemere Formation and the Hutchins Corner Formation.
The Rindgemere Formation consists of "rusty and non-rusty gray to silvery muscovite-biotite-quartz-schist". (Source #2) Muscovite is a gray to silvery mica, and biotite is a black mica. The formation may also include "variably thick interbeds and thin-bedded intervals of quartz-plagioclase-biotite granofels." (Source #2) Plagioclase is a common type of feldspar that is found in granite and many other rocks.
The Hutchins Corner Formation consists of "thin- to medium-bedded purplish gray quartz-plagioclase-biotite granofels with thin interbeds of greenish gray calc-silicate granofels." (Source #2) This formation also has "sporadic zones up to 2 meters thick of rusty-weathering sulfidic biotite-muscovite-quartz schist." (Source #2)
Please visit both outcrops (#1 and #2), then use the information provided in this cache page and Information Sources #1-3 (see links below) to perform the following tasks.
1. a. What type of rock does the first outcrop contain (primarily) - schist or granofel?
1. b. Please give a brief explanation for your decision.
1. c. What is the trend of the bands in these rocks?
1. d. These rocks have a clear pattern of joints (relatively straight fractures) in them. What is the trend of these joints?
2. a. What type of rock does the second outcrop contain (primarily) - schist or granofel?
2. b. Please give a brief explanation for your decision.
2. c. What is the trend (the direction of alignment) of the bands in these rocks?
3. Overall, what do these trends, in the bands and in the joints, tell you about the forces that have been exerted on these rocks? There's no perfect answer for this. And keep in mind that these rocks are by no means in their original positions.
4. Are the rocks observed in this EarthCache part of the Rindgemere Formation or the Hutchins Corner Formation? Please explain your reasoning. (You'll need to refer to Information Sources #1-3, particularly the geologic map, to answer this.)
5. Please describe one geological observation you made at this location that was not already referred to in the EarthCache description. This is to encourage visitors to “think outside of the box” and go beyond the topic that this cache focuses on.
6. Please feel free to post any photos you have taken at this EarthCache, as long as they are appropriate and do not spoil the logging tasks or overall experience for others.
Once you’ve completed your visit, please feel free to log this EarthCache immediately; you do not need to wait until you’ve submitted your logging task responses, and you do not need to wait until you have received a response from the cache owner. However, it would be greatly appreciated if you submit your responses to the logging tasks within 10 days of your visit. Please e-mail your responses to firstname.lastname@example.org and use the GC-code as the subject line.
This EarthCache is at the Great Falls Boat Launch, south of North Windham, on Windham Center Rd., 0.4 miles west of its intersection with River Rd. It is on the east side of the Presumpscot River. The parking area is on the south side of the road. A waypoint has been provided for the parking lot. There is a sign within the parking lot that says "Town of Windham Department of Parks and Recreation – Welcome to FPL Energy's North Gorham Project” (but it is also known as the Great Falls Boat Launch). The parking lot is small and only holds 6-8 cars, so it is best to arrive early in the day, because the parking lot can fill up fast, especially in the busy summer boating months. Please be considerate of other visitors and do not leave your vehicle parked here for an extended period of time. Please do not park along Windham Center Rd., as it would not be safe because there is not much of a shoulder. No restrooms are available here. The EarthCache includes two rock outcrops, which are marked by two waypoints. The outcrops can be reached by walking a short distance south from the parking lot toward the river. One outcrop is at the end of the main trail (the boat launch), and the other outcrop is at the end of a smaller trail that branches off to the right of the main trail. Be careful near the water's edge, especially if you have children with you. While you’re here, why not bring a boat along and do some paddling?
1. Geologic Map of the North Windham Quadrangle, by the Maine Geological Survey: http://www.maine.gov/doc/nrimc/mgs/pubs/online/bedrock/bd-north-windham.pdf
2. Geologic Description of the North Windham Quadrangle, by the Maine Geological Survey: http://www.maine.gov/doc/nrimc/mgs/pubs/online/bedrock/96-16-north-windham.pdf
3. Geologic Description (Map Sidebar) of the North Windham Quadrangle, by the Maine Geological Survey: http://www.maine.gov/doc/nrimc/mgs/pubs/online/bedrock/bd-north-windham-sidebar.pdf
4. Roadside Geology of Maine, by D.W. Caldwell – This series, which covers much of the United States, provides accurate geologic information and is a great source for people developing EarthCaches. Information about the entire series may be found here: http://mountain-press.com/series_detail.php?series_key=2
5. MaineToday.com: http://raisingmaine.mainetoday.com/newsfeatures/0406canoe.html - This page has good information about the boat launch and river, especially for those who want to do some paddling here.
6. Friends of the Presumpscot River: http://www.presumpscotriver.org/ - See this for more information about the river.
7. North Windham Parks and Recreation Department: http://www.windhamweb.com/parksrec/index.shtml- They manage this location.
Thank you to the North Windham Parks and Recreation Department for granting permission to list an EarthCache at these coordinates, which is on land that they manage. (http://www.windhamweb.com/parksrec/index.shtml)
(No hints available.)
Last Updated: on 11/15/2017 3:48:02 PM (UTC-08:00) Pacific Time (US & Canada) (11:48 PM GMT)
Coordinates are in the WGS84 datum