Moraines are long ridges of deposits of glacial till. Terminal moraines are long ridges of debris deposited at the end (toe) of the glaciers. Lateral moraines form along the sides parallel to the glacial valleys. The lateral moraines may join a terminal moraine, forming a horse-shoe shaped ridge. There can be many lateral moraines on either side in a glacial valley. These moraines, partly or fully, owe their origin to the glacio-fluvial waters pushing up materials to the sides of the glaciers. Many valley glaciers, retreating rapidly, leave an irregular sheet of till over their valley floors. Such deposits, varying greatly in thickness and in surface topography, are called ground moraines. The moraines in the centre of the glacial valley, flanked by lateral moraines, are called medial moraines. They are imperfectly formed as compared to the lateral moraines. Sometimes medial moraines are indistinguishable from ground moraines.