How are striations formed?

Striations are a common feature of rocks that have once been overlain by a moving glacier. The scratches on the rock face are generally straight and all are oriented in the same direction, matching the downhill flow of the ice.

As glaciers move, their undersides tend to pick up sand, small stones and other ablative material. As the glacier passes over a stationary rock, these grains scour the underlying rock face, leaving shallow gouges. The marks left on the rocks persist long after the glacier has receded, and the rocks bearing them become telltale signs of the glacial maximums of past ice ages.