If you want it put more concretely, you can travel to Northern Europe and go look at the exposed bedrock that has grooves all over in the same orientation, from

If you want it put more concretely, you can travel to Northern Europe and go look at the exposed bedrock that has grooves all over in the same orientation, from when the glaciers last retreated from that area. They're at sea level. Mountain glaciers are not really what this discussion of glaciers is about. https://en.wikipedia.org/wiki/Glacial_striation https://en.wikipedia.org/wiki/Glacial_striation