Glacial striations are scratches or gouges cut into bedrock by glacial abrasion. These scratches and gouges were first recognized as the result of a moving glacier in the late 18th century when Swiss alpinists first associated them with moving glaciers. They also noted that if they were visible today that the glaciers must also be receding. Glacial striations are usually multiple, straight, and parallel, representing the movement of the glacier using rock fragments and sand grains, embedded in the base of the glacier, as cutting tools. Large amounts of coarse gravel and boulders carried along underneath the glacier provide the abrasive power to cut trough-like glacial grooves. Finer sediments also in the base of the moving glacier further scour and polish the bedrock surface, forming a glacial pavement. Ice itself is not a hard enough material to change the shape of rock but because the ice has rock embedded in the basal surface it can effectively abrade the bedrock

https://en.wikipedia.org/wiki/Glacial_striation

By Walter Siegmund - Own work, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=2500400