Have I ever told you about glacial polish? It works just like sanding a piece of furniture. We would start with a coarse grit and move toward finer grits as we work toward completing a wooden box so it has a smooth finish. Glaciers do not plan ahead like we do. They throw everything they have at the bedrock mountains in their way. Boulders, silt, sand, and gravel all help erode away the bedrock beneath a glacier, but very slowly. In some areas, you can see striae or striations (I haven’t found a consensus on which term is preferred), showing where glaciers with rocks frozen into their base scratched the bedrock. You may see chatter marks or crescent gouges where boulders smashed into the bedrock surface. But polish requires a fine grit, for example silt, to wear away at the rock until it shines! I think the bedrock was marble in this location, so that might be why the erosive features show so clearly.