Layers of History, peek-a-boo through the trees
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This is on private land so bring your Binos or long camera len to view the area. Park on the wide tar shoulder of the road and view this earthcache trough the trees. Do NOT go into this area, no permission was secured. You will view this earthcache from approx. 300 feet away.
A special Thank you goes to Northwoods Explorer for his technical expertise in assisting with this EarthCache.
Roadside Geologic History
This roadside earthcache takes a long look at the geological history of this section of Maine.
The walls of this abandoned quarry represent the current stage of a very long and dynamic geologic history of the region. The rock that makes up the walls are classified as metamorphic rock, which means that at one time it was affected by heat and pressure deep inside the earth which has significantly changed its form. Before metamorphism it was sedimentary rock, which had formed originally by hardening of deep-sea sediment (sand and mud) into rock, this can be identified by the layers that you can see from the road. After metamorphism, continued geologic stresses on Maine's bedrock crust have produced fractures (faults and joints) cutting through the rock mass in various directions, these can be identified as the white veins or dikes in the walls. Finally you can see the results of the glacial period as the unconsolidated glacial deposits that used to cover the bedrock at the top edge of the rock walls. What will follow is a very brief outline of the geologic events that affected this part of Maine; please note that these processes while very slow reflect a history that covers an immense span of geologic time.
During the Silurian Period (420 million years ago) sediment accumulated in a deep ocean basin. This basin lay between the edge of North America to the west and an ancient small continent to the east, the microcontinent called Avalon. As the layers accumulated one on the other, some were deposited individually with sharp boundaries between them, and others were deposited as mixed masses in graded beds that change gradually from the bottom to the top of the layer. Then during the Devonian Period (405 -380 million years ago) as the Avalon microcontinent moved slowly toward the North American continent by plate tectonic motion, the Silurian sediments of the intervening ocean became severely compressed and deformed. The earth's crust in this collision zone became thicker as it was squeezed, producing a great mountain range. The layers were contorted into folds. Microscopic mineral grains became aligned to produce a rock cleavage, a wood-like "grain" along which the rock splits into sheets and splinters. Minerals in the rock recrystallized under the prolonged heating to grow slowly into metamorphic turning mudstones into phyllite and turning sandstones into quartzite. Many of the white veins here were produced during metamorphism as hot fluids containing dissolved silica circulated through small open spaces in the rock, leaving small quartz deposits. These are the very narrow white bands of rock seen from the road.
During the Carboniferous Period (290 million years ago) the movement changed to a sideways direction. The rocks had cooled since the Devonian, because the geologic features of this age are typical of brittle deformation in which the rocks broke rather than folded. Along this fault, the rock was obviously broken as the south side of the fault moved toward the west in relation to the north side. At the same time, some straight, vertical fractures opened in the rock and were filled with quartz to produce long, white veins. During the Mesozoic Period (200 million years ago) began the formation of what we now call the Atlantic Ocean. The Atlantic did not open along a clean break. Rather, the whole neighboring region of crust contains numerous extensional fractures. Magma (molten rock) from the base of the earth's crust erupted through these fractures, and solidified into thin sheets of rock called dikes. Dark-colored Mesozoic dikes, typically a foot or two thick, are common in this area. Then the glaciers did their work where erosion has removed the upper few thousand feet of the earth's crust allowing us to look at rocks that were affected by geologic processes deep in the earth and over a long span of time. While as it melted it left a thin layer of till that we see it the top of the quarry.
At the posted coordinates you will find yourself at the entrance to an abandoned quarry used to make road fill for the interstate. It is easy to see the layers formed during the various time period and it should be easy to see why a geologist would find this location interesting. Normally when we see this type of excavated rock wall, we see horizontal layers, but this has very noticeable Vertical dikes that I found interesting... Remember this is an earthcache so there is no container just an earth science lesson at an amazing bedrock feature. In order to fulfill the requirements of this earthcache you need to: email through my profile the estimated height of the quarry wall and the estimated width of each of the 4 vertical white dikes or intrusions that are grouped together as if they are almost equally spaced apart, (near a large diagonal dike). The estimated average width of the large diagonal dike? Please be sure to include the name of the earthcache in your email. After answering the questions to log this cache, you must post a photo with your GPS and a recognizable feature of the quarry in the background.
If for any reason you seem to have difficulty seeing the 4 dikes grouped together, chances are it is a very bright sunny day shining directly on the rock wall, hence Binos or long camera lens should help. Otherwise just an hour or two should make viewing this location easier at times.
FTF HONORS GO TO THE FTF GEOMOBILE OWNER TH!!! Nicely done!
Additional Hints
(Decrypt)
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