- Killas
Killas is a Cornish
mining term formetamorphic rock strata ofsedimentary origin which were altered by heat from the intrudedgranites inCornwall ,England .Origin of killas
The deposition of the killas strata is spread over the
Devonian andCarboniferous geological periods. Thesediment s are not evenly spread over the county, with the Carboniferous beds being only found in the far north of Cornwall.The depositional environments of the killas were very varied, as is revealed by the
fossil content and the sedimentary sequences. The fossils indicate changes from ocean basin environments to shallow sea environments. The well knownDelabole Butterfly formation was found in the upper Devonian beds of North Cornwall.Shortly after the deposition of the sediments, the
Variscan orogeny caused the intrusion of theCornish granites and the subsequentcontact metamorphism created the metamorphic rocks seen today. This also put intense pressure on the sediments causing them to be folded and faulted. This is most apparent in the cliffs atMillook Haven on the north Cornwall coast, where the cliffs display an impressive series of angular recumbent folds.Economic uses of killas
Killas underlie two thirds of Cornwall and, as a result of
hydrothermal mineralization from the granites, contain the majority of the minerallode s or veins which at one time provided up to half of the world'stin andcopper , and economic prosperity to Cornwall. Of lesser economic importance, the stone itself is an important building and roofing stone in Cornwall, the largest single source in the county beingDelabole slate quarry, which has provided a high quality stone for at least six centuries.
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