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[[Image:Blaenau.jpg|right|thumb|500px|The landscape surrounding Blaenau has been blighted with millions of tons of spoil. These slag heaps arose mainly as a result of 19th century mining techniques, and unfettered capitalistim.]]

[[Image:Blaenau.jpg|right|thumb|500px|The landscape surrounding Blaenau has been blighted with millions of tons of spoil. These slag heaps arose mainly as a result of 19th century mining techniques, and unfettered capitalisim.]]

'''Blaenau Ffestiniog''' is the capital of the Welsh  [[slate]] quarrying industry. The slate-bearing strata of Ffestiniog belong to the [[Ordovician]] or Lower [[Silurian]] systems, and are of an uniform soft blue-grey colour, although the North Vein or topmost bed shows a tendency to be slightly darker. The chemical analysis of a standard Ffestiniog slate shows silica 55 per cent., alumina 25 per cent., iron oxide 11 per cent., the remainder being composed of various elements of which the chief is magnesia. The lime contents - an excess of which often characterises an inferior slate - are negligible. <ref>For a more detailed account, see: http://www.llechicymru.info/t000952.cymraeg.htm</ref>.  

'''Blaenau Ffestiniog''' is the capital of the Welsh  [[slate]] quarrying industry. The slate-bearing strata of Ffestiniog belong to the [[Ordovician]] or Lower [[Silurian]] systems, and are of an uniform soft blue-grey colour, although the North Vein or topmost bed shows a tendency to be slightly darker. The chemical analysis of a standard Ffestiniog slate shows silica 55 per cent., alumina 25 per cent., iron oxide 11 per cent., the remainder being composed of various elements of which the chief is magnesia. The lime contents - an excess of which often characterises an inferior slate - are negligible. <ref>For a more detailed account, see: http://www.llechicymru.info/t000952.cymraeg.htm</ref>.