Morrow Mountain - Argillite Tells a Tale EarthCache
Morrow Mountain - Argillite Tells a Tale
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The Uwharrie Mountains lie on the eastern edge of the Piedmont plateau, forming a barrier of steep hills and ridges between the Coastal Plain and the gently rolling Piedmont.
The Uwharries are the oldest mountain range in North America. Thought to have once peaked at some 20,000 feet, erosion has worn the Uwharries to a peak height of only 1,119 feet. The Uwharries are part of a larger geologic formation called the Carolina Slate Belt. Composed of slightly metamorphosed volcanic and sedimentary rocks, the belt extends from central Virginia to central Georgia. Geologists believe that the belt was part of a volcanic island chain in a shallow sea off the North American continent about 600 million years ago. Layers of volcanic ash, lava, and sediment were deposited in this sea. Later, they were deeply buried, folded, tilted on edge and finally exposed at the earth’s surface. Today the harder metavolcanic rocks form the mountain peaks, while the softer metasedimentary rocks line many of the stream valleys.
Argillite deposits in the park show evidence of the process that created this once mighty mountain range. Argillite formed in the quiet waters where finer sediments such as volcanic ash and silt had time to settle to the bottom. Once there, the weight of water and overlying sediments helped compact and cement these soft muds into a fine-grained sedimentary rock. Later, this mud-stone was deeply buried and slightly metamorphosed to create the argillite we see today. Argillite contains parallel layers representing the layers of ash and silt laid down in the ancient sea. These layers were laid down horizontally one upon the other throughout millions of years. Between 250 and 500 million years ago, after the argillite had already formed, the crustal plates carrying Africa and North America moved together pushing up the underlying layers and forming the Uwharrie Mountains. During this mountain forming process, large sections of argillite were folded, faulted, and tilted then eroded over millions of years exposing the argillite at the earth’s surface. These exposed layers give us a view of the force involved in forming this mountain range.
The posted coordinates will take you to the old quarry site in the park. From here, argillite was mined and used as a building material for various structures in the park.
To claim this Earthcache:
1. You must identify and photograph the layers of argillite visible in the quarry. Post this picture with you and your GPS in your log.
2. Also, answer the following in an email: What approximate angle are the layers at and why are they no longer horizontal?
Please do not post answers in your log. As always, obey all park rules and practice leave no trace ethics.
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