The Wolds comprise a series of low hills and steep valleys underlain by calcareous (chalk and limestone) and sandstone rock, laid down in the Cretaceous period. The characteristic open valleys of the Wolds were created during the last glacial period through the action of glaciation and meltwater. The chalk that underlies the Chalk Wolds Landscape Character Type extends from the Yorkshire Wolds to the south coast of England, in East Sussex and in Dorset. Geologically, the Lincolnshire Wolds is a continuation of the Yorkshire Wolds which runs through the East Riding of Yorkshire; the point at which the ranges of hill crosses the Humber is known as the Humber Gap.