The purpose of drumlin formation is to facilitate glacier flow. Drumlins form in a deforming layer between ice and ground, they produce a pimpled ground surface which causes less drag in the flowing system, after the fashion of the Prandtl effect which reduces boundary layer detachment (as in the flying golf ball). This pimpled surface has selforganising properties and this causes the development of a low drag situation. The drumlin field is the critical phenomenon; the formation of individual drumlins is a small part of the overall effect.