Een bijzondere vuursteenknol

The 'Silex conique' or 'festons' describ'ed by Lemaitre (1965) from the coast near Vaucottes departement Seine Maritime, are not to be traced back to very Large siliceous sponges. All the specimens studied by me and found by me, in the Chalk along the French Channel-coast, and in the southern part of Limburg and adjacent areas, are chertconcretions originated round Large tracks made by burrowing. These tracks mostly occur more or less vertical but can also occur more or less horizontal. The length of the former varies from .3 - 5 metres that of the latter exceed 10 metres. I cannot explain by which organism the track has been made as this type of track is not known to me from references.