Chalk produce, and thus widely used in the developing world, calcium-based chalk can be made where the crumbling particles are larger and thus produce less dust, and is marketed as "dustless chalk". Colored chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often colored), used to draw on sidewalks, streets, and driveways, are primarily made of gypsum. Chalk is a source of quicklime by thermal decomposition, or slaked lime following quenching of quicklime with water. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines,
Chalk stream which would normally be too large for the term "stream". The Somme River in Northern France is a chalk stream on a larger scale. Chalk streams of the Southern England Chalk Formation in Berkshire, Hampshire, Wiltshire, and Dorset: Chalk streams of the Southern England Chalk Formation in the Chiltern Hills and Hertfordshire (tributaries of the River Thames, River Lea and River Colne): Chalk streams of the Yorkshire Wolds: Chalk streams of Lincolnshire: There are several chalk streams in the Lincolnshire Wolds including Chalk streams of Kent: Chalk streams of Surrey: Chalk streams of Norfolk: Chalk stream Chalk streams are streams