Tills are described which occur in ridges and mounds arranged both parallel and transverse to the flow direction of the depositing glacier. Field localities are drawn from the English Midlands, Western Canada, and south Victoria Land, Antarctica. It is shown that ridges and mounds cannot be explained in terms of preferential till accretion. An alternative mechanism is presented in which form and structure are a result of redistribution of debris in transport by secondary flows in ice. Debris entrainment by Antarctic cold-based glaciers Is explained by consideration of the morphology and sedimentology of the ice margin and the pattern of glacier flow.