At Elsloo near the River Maas, resting directly upon older Tertiary deposits, is a bed of glauconitic, more or less lithified coarse sand and gravel. The layer containing the most gravel is especially rich in fossils. From a single cubic metre some 1,000 fish teeth, almost as many internal moulds of shells and snails and skeletal remains of whales and seals have been collected. Remarkable is the large number of shark's teeth. All in all this is a hotchpotch of all kinds of material derived from a much larger area. This is also indicated by the fact that a high percentage of these fossils are more or less abraded and worn: the sharp edges have become smooth by rolling over the sea floor and rubbing together.