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Geology near the Augusta Civic Center
Augusta has many generally accessible localities to examine many aspects of local geology. One such locality is within and around the large retail complex associated with the Augusta Civic Center. With many large parking lots, the area is generally accessible for viewing some interesting aspects of Maine's geology.
Near the Augusta Civic Center (Figure 1) are excellent exposures of the metamorphic and igneous rocks that are found throughout this area of the state.
While there is great variety in the igneous rocks exposed throughout Maine, a primary type in the Augusta area is granite (Figure 3). Granite is an intrusive igneous rock. That is, a molten lava intruded into the crust at depth and cooled there to form solid rock. Eons of erosion have now exposed the granite at the surface. In this particular granite, the primary minerals quartz and feldspar are nearly equal in size, giving the granite a texture that geologists describe as equigranular (Figure 4). The granite here is also interesting because it contains two kinds of mica - the white mica is called muscovite and the black mica is called biotite. By mapping around the area, geologists have established that the granite cuts across the metamorphic rocks, indicating that the granite is younger. It's around 400 million years old.
The exposures of granite here are full of fractures that are nearly parallel to the surface of the earth. There are a few vertical fractures as well. These fractures are the primary routes taken by groundwater as it flows through the rocks. When a driller drills a well into the solid bedrock, the water in the well comes from these fractures. In these outcrops, ice forms in the winter where groundwater flows to the surface along these fractures, clearly showing which ones are the important water-bearing fractures.
Text and photos by R. Marvinney
Originally published on the web as the February 2003 Site of the Month.
Last updated on April 19, 2012
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