On Some Sources of Error in the Study of Drift

Abstract

As a general rule we may feel sure that the boulders scattered over the surface of a district which consists chiefly of boulder clay, have been derived from the underlying deposit. There are, however, some cases in which the inference is unsafe. For instance, the Thames now marks the southern limit of the glacial drift—a curious circumstance, and one of which a wholly satisfactory explanation has not been given. Many think that this sharp definition of the southern limit of the glacial drift is so improbable that they would fain attribute some deposits in North Kent to the glacial period, or at any rate would expect to find a few sporadic boulders stranded on the slopes of the North Downs; and there far-transported fragments do not unfrequently occur.