Sometime after the last retreat of the ice in the Quaternary ice age, the Scandinavian peninsula was separated on the south from the north German plain and Denmark. Later, England was cut off by the Channel from the continental land mass. An estimation of the times at which these two events happened is interesting to archaeologists, botanists and zoologists alike, because the communities with which they are concerned are affected by the barrier of an intervening arm of the sea.

So far most of the evidence about the times of separation comes from botanical and archaeological sources, from pollen analysis and the investigation of cultural sites. In this paper the distribution and physiology of certain freshwater animals are used to provide argument that the separation of Scandinavia and of England could only have taken place at times of particular climatic conditions. The climatic definition of the times of separation makes it possible to fit them in to the absolute geochronological scale which has been established by Scandinavian workers.