The Geology of Devon and Cornwall, England

The county of Devon gave its name to the Devonian geologic time period. Running throughout the north and south of Devon and continuing into Cornwall, the massive limestone deposits were the first to be extensively studied and recognized as dating to this specific time period based on the fossils contained in the limestone. This rock was deposited in warm seas with coral reefs and abundant life. It is older than the rocks exposed along the Jurassic Coast representing a time when most life was still in the seas. Reaching back from 359 to 416 million years ago, the fossils found here include trilobites, ammonites, corals and the abundant brachiopods.

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These rocks are greatly disturbed in some of the interior areas of Devon, faulted, folded, and cut through with beds of volcanic ash and massive intrusions of granite. The most extensive section of igneous rock in southwest England and the largest deposit of granite in Britain is found in Dartmoor National Park in central Devon. A vast area of granite was intruded into the surrounding rocks during the Carboniferous period during a time of geologic activity about 300 million years ago. Erosion has now exposed the granite in much of the area. Tors, tall spires of exposed granite, dot the moors while low areas are covered with peat deposits used as fuel for centuries. The tors are a highlight of the Dartmoor Park; large hills of durable granite are topped with odd outcropping formations. The highest points here are the tops of the tors, some in excess of 2,000 feet in elevation. Abundant rain in the Dartmoor area has lead to the development of vast peat deposits. Made from centuries of sphagnum moss growth, the bogs and peat deposits cover much of the granite in the low-lying areas.

Quarries, where many of the rocks in the area are mined, abound. Granite, sandstone, metamorphic rocks, and limestone have been used since prehistoric times for monuments, buildings, and religious structures. Along with quarrying, the ancient inhabitants of Britain mined tin and copper in Devon and Cornwall as well. During the Bronze Age, copper and tin were of high value for fashioning weapons, tools, and ornaments. With the addition of a small amount of tin to the copper, a much more durable alloy, bronze, could be produced. Along with these two metals, silver, zinc, and arsenic were also mined in this region. Although no mines are active today, this was an important part of the history of the region. Cornwall was one of the most valued sources of metals in Europe. Without the heated intrusion of the granite into the area, there would have been no mineral mines.

During the Ice Ages of the Pleistocene era, the southwest of Britain was one of the few areas to remain unglaciated. The soils in this area are much older than in other parts of Britain as they remained relatively undisturbed during this time by the heavy sheets of ice expanding down from the north.

The geology of this area is responsible for its scenery, much of its history, and has brought wealth to the area from historic mines and modern tourism.