Erratics selection index as a value determining the origin of marginal forms and glacial sediments.

The composition of erratic assemblages depends to a large extent on the specific gravity of the particular erratic boulders. The observed dependence may be explained as a result of a selection within an erratic assemblage by glacifluvial waters. The index is the ratio of the Aland erratics (acid - hence lighter ones) to the basic and ultrabasic ones (heavier). -after Author