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An earthcache in beautiful Harriman State park
Before we go ahead with the Earthcache - we would like to thank the
Sebago Beach Park Manager and staff for working with us to develop
a permit for this special type of cache - they were very helpful
and easy to work with.
Approximately 600 - 700 million years ago the North American
continent developed a rift (a tear in the earth’s crust that
continuously erupts magma and pushes the two sides apart) and began
splitting apart, each side moving in the opposite direction of the
other. As this occurred the area between the two land masses filled
with sediments and volcanic deposits (from the magma at the rift
zone). Over time sea level rose and much of New York was covered by
this ancient shallow sea known as the Iapetus Ocean.
Then the rifting ended. The ancient sea began to close and our
continent collided with the island arc that had developed during
the rifting process. This event is called the Taconic Orogeny (or
mountain building event). During this event the sedimentary
deposits that made up the shorelines were scraped off and thrust
onto the continent as the rest of the mass was forced deep into the
earth. Following the Taconic Orogeny was the Acadian Orogeny which
occurred roughly 400 million years ago. This tectonic event also
altered the landscape through active folding and faulting of the
entire area.
The final orogenic event to affect this area is known as the
Alleghany Orogeny which began about 300 million years ago. The
Alleghany Orogeny, also known as the Appalachian Orogeny, resulted
when Africa and North America collided forming the super continent
Pangaea. The belt of mountains that extends from southern New York
southward into Alabama is the result of this tectonic collision. As
each of these mountain building events occurred, immense areas were
folded, faulted and refolded, metamorphosing rocks that had already
been altered during the previous events. It was during the
Alleghany Orogeny that the features we see today in the Hudson
Valley began to form.
So, after all of this intense tectonic activity – what do you get?
Well due to these events, in New York, and throughout New England,
we’re very lucky to have a wide variety of rocks to explore. As you
travel through Harriman State Park, you have an opportunity to see
some of the oldest rocks in the area. These rocks offer a window
into the intense geologic history of this area.
There are three main classes of Rocks – Sedimentary, Igneous and
Metamorphic.
The classification is done based upon how they originated. The
“rock cycle” helps us understand these classifications a little
better. Igneous rocks or “fire rocks” form as a body of
magma cools. Once this or any other type of rock is formed, over
time, they are eroded into smaller particles or sediment. These
particles are deposited and are eventually compressed and hardened
into sedimentary rocks. In some instances these rocks are
buried and exposed to high temperatures and pressures. The results
of this heat and pressure are metamorphic rocks.
The cycle may continue if these metamorphic rocks are heated and
compressed again and melt, then the molten rock might eventually
form another igneous rock. Sometimes if you look you are able to
see a transition zone where the temperatures and pressure exerted
upon the rocks changed. For example, if a rock cools slowly the
crystals grow nice and large and are easy to see but, if the
temperature and pressures change you would notice a difference in
the appearance as the mineral crystals get smaller and harder to
distinguish. Two examples of rocks you may find are:
GNEISS
Gneiss is a high grade metamorphic rock. This means the rocks had
been forced so far below the surface of the continental crust that
they were subjected to intense temperatures and pressure that
altered their chemical make-up, known as “metamorphism”. At these
intense pressures and temperatures the rock becomes “rock taffy”
and gets stretched and twisted into folds. Materials that are
similar in makeup begin to band together and once cooled, form
wonderful pink and green gneisses (pronounced “nice”) with
pronounced layering and banding.
The minerals that compose gneiss are the same as granite. Feldspar
is the most important mineral that makes up gneiss along with mica
and quartz. Gneiss can be formed from a sedimentary rock such as
sandstone or shale, or it can be formed from the metamorphism of
the igneous rock granite.
GRANITE
Granite is the most common type of intrusive igneous rock at the
Earth’s surface. Granite is an igneous rock that consists of quartz
plus feldspar, with or without a wide variety of other minerals
(accessory minerals). These minerals are quartz, feldspar, mica,
and usually hornblende. Granite forms as magma cools far under the
earth's surface. Because it hardens deep underground it cools very
slowly. This allows crystals of the four minerals to grow large
enough to be easily seen by the naked eye. The quartz and feldspar
generally give granite a light color, ranging from pinkish to
white. But that light background color is punctuated by the darker
accessory minerals.
Between them, Granite and Gneiss share the same basic and some
accessory minerals. Those minerals include quartz, feldspar,
hornblende, biotite.
Quartz is the second most common mineral in the Earth’s crust,
second only to Feldspar. Quartz is a common component of granite,
sandstone, limestone, and many other igneous, sedimentary, and
metamorphic rock. Depending upon the variety of quartz it may
present in many different colors. Typically, quartz found in
granites and gneisses tend to be white in appearance.
Feldspar is the name of a group of rock-forming minerals which make
up as much as 60% of the Earth's crust. Feldspars can be found in
igneous, metamorphic and sedimentary rocks and are typically broken
up into two groups - potassium based Alkali Felspars (K-spar) and
sodium based Plagioclase Feldspars. Feldspar can come in a variety
of colors - reds, pale pink, whites and grays - among others.
Unfortunately, color is not always an easy tool to use to deterine
which type of feldspar you are looking at.
Hornblende is a very common amphibole mineral. It is usually black
but can also be dark green or brown. It is a common primary mineral
in granitic rocks and a common metamorphic mineral in gneiss and
schist.
Biotite is a common rock forming mineral, being present in igneous
and metamorphic rocks. Biotite is typically black to brown in
color, but may come in other colors as well.
So, after alllllllll of that reading WHAT do you need to do for
your smiley??
THE CACHE IS AT THE SEBAGO BEACH AREA - DURING THE OFF
SEASON THE AREA MAY BE CLOSED OFF AND YOU MAY HAVE TO WALK IN FROM
A DIFFERENT DESIGNATED PARKING AREA. DO NOT PARK ALONG THE ROAD -
YOU WILL GET A TICKET.
Once you arrive at the IP take a look around – these are some very
cool and very old rocks. Using what you have read above do the at
least 2 of following :
Part 1: Determine what type of rock you are looking at……as you walk
toward the outcrop, head to the right side of the rocks…this may
help you figure it out. We’ll give you a hint – Granite or
Gneiss.EMAIL the answer.
Part 2: Now look a little closer and find some hornblende or
Feldspar – take a photo of the mineral with your GPS next to it –
nice and close so we can really see it.
Part 3: OK – this part takes a little more work. Walk back and
forth in front of the outcrop. As you do this you will notice
changes in the rock face and at one point you can see almost see an
area or zone where the type of rock appears to change from one to
another. Take a picture of this "transition" zone as well.
As with all of our EC’s, we aren’t looking to delete smiley’s for
incorrect answers or photos – we really just want you to have fun
and learn something new about this area. As long as you read the
material and we see you tried to find the corresponding area, we
won’t delete your smiley.
Additional Hints
(No hints available.)