In the northern part of The Netherlands during the Saalian glaciation numerous Scandinavian rocks have been deposited. One of the most interesting rocks is the so called 'baksteenkalk', a Upper-Ordovician, Caradocium, (units C2 to D1) chalk in which fossils of ten different groups are found. The chalk is often silicified and weathering causes a bricklike (baksteen) structure. The most important area of origin is a triangle between North-Gotland - the southern Åland Islands and Stockholm.