The large no ordinary mud mounds were discovered in summer 1993 in the Lower Ordovician Volkhov stage limestones of the Putilovo quarry. The mud mounds have sparitic flanks, micritic crusts and a clay in their cores. We suggest to call them the "Hekker-type mud mounds". There is a possibility that little sinsedimentary humps discovered under the Ivangorod fortress and in the Kingisepp quarry are embryonal forms of the Hekker-type mud mounds. The humps are very similar to the sedimentary
folds" that were described in Sweden by M. Lindslrom.
