A winegrowing terroir is the combination of an identifiable physical and biological environment (soil, subsoil, relief, climate). The chalky subsoil (chalk, sand and chalky marl) facilitates soil drainage and the mineral character of certain Champagne wines. The Champagne chalk is composed of the skeletons of marine micro-organisms and molluscs’ fossils from the secondary era (Cretaceous). It is very porous. Thus, it constitutes a genuine water reservoir that provides the vines with a sufficient supply of water even during the driest summers.