De mollusken van de holocene fluviatiele afzettingen bij Hekelingen (Spijkenisse, Zuid-Holland)

During archaeological excavations at Hekelingen, 14 km SW. of Rotterdam, 72 species of land- and freshwater molluscs were found. The deposits sampled were formed in the estuary of the rivers Rhine and Meuse in the first half of the Subboreal (Calais IV) period. The age is therefore about 4500 years BP. The presence of Pisidium personatum, Viviparus contectus, Mercuria confusa, Marstoniopsis scholtzi, Vertigo alpestris, V. moulinsiana, V. pusilla, V. substriata, Balea perversa, Cochlodina laminata, Macrogastra ventricosa, and Helicigona lapicida, is either new for or rare in the Dutch Holocene. The molluscs are indicators of an environment now totally absent in The Netherlands. In a freshwater tidal area a broad creek yielded flowing fresh water; quiet waters and marsh also occur. The levees along the creeks were under woodland. Well developed trees, shrubs and herbs were present. There was a great variation in environment. This part of the river valley was situated not far from the sea (in the west). Apart from high humidity, the mean summer temperature was a little higher than today.