“The moral virtues, then, are produced in us neither by nature nor against nature. Read more about this topic: Tor (geography)įamous quotes containing the word formation: Weathering has also given rise to circular "rock basins'" formed by the accumulation of water and the repeated freezing and thawing – a fine example is to be found at Kes Tor on Dartmoor. Eventually the granite is weathered down to a level equivalent to sandy gravel, known as growan, which consists of individual crystals.
Finally during the ice age the majority of the rotted granite was stripped away and the freeze-thaw cycle levered away larger blocks, leaving them scattered around the now-exposed tors as clitter, where they have provided ready building materials for thousands of years.
The rocks that overlaid the granite pluton were eroded quickly (in geological terms) and the consequent release of pressure caused the formation of sub-horizontal joints which tended to follow the shape of the land and which started the separation of the upper part of the pluton into blocks of varying sizes.įurther chemical attack by circulating water and later by acidic rainwater caused further weathering along the lines of these joints, resulting in the more or less complete decomposition of the granite into its constituent crystals in regions where the joints were closely spaced. They are the result of millions of years of weathering.įor example the Dartmoor granite was emplaced around 280 million years ago and as it cooled it contracted leaving a multitude of mainly vertical cracks these facilitated hydrothermal circulation which both chemically altered the rock surrounding the cracks and deposited minerals in them. Tors are usually composed of granite or metamorphic rocks, but they can also develop in volcanic rocks and occasionally other hard rocks such as quartzite.
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