Creosotes are a category of carbonaceous chemicals formed by the distillation of various tars, and by pyrolysis of plant-derived material, such as wood or fossil fuel. They are typically used as preservatives or antiseptics. Some creosote types were used historically as a treatment for components of seagoing and outdoor wood structures to prevent rot (e.g., railroad ties and bridgework, see image). Samples may be commonly found inside chimney flues where the wood or coal burns under variable conditions, producing soot and tarry smoke. Creosotes are the principal chemicals responsible for the stability, scent, and flavor which is characteristic of smoked meat; the name is derived from the Greek kréas (κρέας), meaning ""meat"", and sōtēr (σωτήρ), meaning ""preserver"".The two main kinds recognized in industry are wood-tar creosote and coal-tar creosote. The coal-tar variety, having stronger and more toxic properties, has chiefly been used as a preservative for wood, while the wood-tar variety has been used for meat preservation, ship treatment, and for medical purposes as an expectorant, antiseptic, astringent, anaesthetic, and laxative, though these have mostly been replaced by modern medicines. Coal-tar creosote was formerly used as an escharotic to burn malignant skin tissue and in dentistry to prevent necrosis before its carcinogenic properties became known. Varieties of creosote have also been made from both petroleum and oil shale and are known as oil-tar creosote when derived from oil tar and water-gas-tar creosote when derived from the tar of water gas. Creosote also has been made from pre-coal formations such as lignite, yielding lignite-tar creosote, and peat, yielding peat-tar creosote.