The bed-thickness of sedimentary beds and its frequency distribution in a geological body have been treated to show a lognormal distribution. In this paper it is discussed on a basis of a model presented by a great Russian mathematician, Prof. Kolmogorov, A.N. who said that a sedimentary bed has a thickness of so-and-so cm, but in some cases, it has a negative thickness. Actually, the presence of a washed -out phenomena will erode the pre-existing sedimentary layer, and sometimes the pre-existing will completely disappear. For such a washed-out bed, Kolmogorov described that it has a negative thickness. In this paper, an example for the Neogene Kakegawa Formation and its bed-thickness is presented, and additionally the bed-thickness of varved diatomite in the Hiruzenbara Formation of Okayama Prefecture is noted as an example of rather accumulative type of sedimentation.