Friday, July 15, 2011

Off the Coast Continued

The winds have picked up a bit so I'm off the rocks for a bit.  Speaking of rocks, that's one of the highlights of our Maine Coast visit.  The rocky coast of Maine is famous.  The mountains rally do go down to the sea here.  The geology is to dream about.  Granite, schist, tilting, glaciers, extrusions, uplifting--you name it and you can find it here.

Most of the layered rock is metamorphic in nature.  The layers show how the silts and sands were laid down and then heated and compressed into the layer schist rocks shown in the pictures.   The seams of granite, an igneous rock flow through the layers of schist all along the coast.  The colors and textures are incredible and make a day on the rocks always exciting, always beautiful and always induce thoughts of formation and changes to the Earth.  It is hard not to wonder how the patterns were formed.  I know the basic geology, but it is still fun to consider the order or chronology of the formations I am climbing upon. 

The different colors come from the various minerals that were added to the melted raw materials of the granite.  Granite with medium-sized white grains of the mineral feldspar as well as larger grained igneous rocks called pegmatite can be seen.

 A very good description of these formations is on the following site:  Maine Geologic Survey of Pemaquid Area

Metamorphic Rocks

Metamorphic rocks make up the bulk of the bedrock. The thin stripes or bands on the rock surface are actually the edges of layers. Layers of different color are made up of different combinations of minerals, although the individual mineral grains are quite small (about 1/32 inch), so they may be hard to pick out with the naked eye. The medium gray layers are composed of quartz, feldspar, and black mica (biotite) grains. Layers with a greater proportion of biotite are darker colored, even black. Still other layers have a greenish color because they contain the mineral diopside in addition to the pale gray or white quartz and feldspar. Taken as a whole, metamorphic rock with this sort of layered structure is called a gneiss (pronounced "nice"). The layers were originally deep sea sediments of muddy sand and silt (the gray and black layers) or limy sand and silt (the green layers). They have been changed by heat and pressure into the metamorphic rocks we now see. This process of change (called metamorphism) occurred in the Devonian Period of geologic time, between 360 and 415 million years ago. At that time these rocks were at depth in a geologically active mountain system. The deposition of the original sediments occurred before then (in the Silurian Period), about 430 to 440 million years ago. 

The above specifics of the geology help to explain how our Earth changesThe wanderings on the rocky outcroppings help to inspire the wonder of change and the at the same time the constancy of how stable this formation seems to be.  Every year when I return to this area of Maine I am mesmerized by the beauty of its geology.  Every day I climb the rocks and ledges, and every day I find new formations, different grain patterns and a spectrum of colors.  It is why I am a naturalist at heart.

Of course, I'm not the only wanderer here.  the gulls come and sometimes even leave evidence of dinner.
I also love to find the colors of biology in and on the rocks.  the lichen reminds me that even these substantial, seemingly permanent formations are temporary.  The lichens will attach, grow, secrete and help to wear down the rocks.  Of course, I won't see these big changes, but I know they are happening.  See the world of the rocky coast of Maine is NOT static.  It is dynamic just like I started with.  The changes will come slowly, but I know they are happening.  I'll just have to come back next year to see the differences (and the sameness too!)


Stewart M said...

Hi (again) - those rocks remind me on the rocks on the beaches in Tasmania. The lichens are similar as well!


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