A winegrowing terroir is the combination of an identifiable physical and biological environment (soil, subsoil, relief, climate). The Champagne chalky subsoil facilitates soil drainage. In places, it is made up of seven different layers (chalk, sand, clay, limestone, etc.) 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.