Glacial striations
Glacial_grooves.jpg
Glacial striations or glacial grooves are gouges or grooves cut into the bedrock by glacial ice and meltwater as it slowly ground its way along during one of the Earth's Ice Ages or by mountain glaciers. Striations usually occur as multiple, straight parallel lines representing the movement of the sediment loaded base of the glacier. Large amounts of gravel and boulders were carried along and provided the scouring power to cut these grooves into the bedrock. Fine sediments in the base of the moving glacier scoured and polished the bedrock.
One very good example can be found at the National Natural Landmark at Glacial Grooves, Kelleys Island, Ohio which is 400 feet long, 15 feet deep and 30 feet wide. An much longer nearby groove on the island, the Great Grooves, was quarryied out in the early 20th century. Those grooves were also about 15 feet deep and 30 feet wide but were 2000 feet long.