 It was renamed 'dark earth' because of confusion with the "chernozem" (black earth soils in Russia), whose dark colour is traditionally (not universally) thought to come from humus, rather than soot.In the Hebrides, it was customary to remove the thatch from the "black houses" every spring, and spread it on the fields as fertilizer, improved by the soot which it retained.On Achill Island, special smoke huts were built in the fields, stone structures with sod roofs.