Glaciers shape the landscape by means of erosion, which manifests itself as abrasion and deposition. Ice loaded with rocks and minerals slides along like coarse sandpaper. Evidence on bedrock outcrops appear as scratches, or striations. On a large scale the process is called quarrying or plucking. Often tapered, blunt nosed hills called whalebacks are formed. Another result is the excavation of basins which become lakes. Terms associated with deposition are till (unsorted debris), moraines (distinctive landforms), drumlins (streamlined hills with long axes parallel to the ice flow), kames (conical hills), and kettles (collapse pits formed when buried ice melts). Belts of lakes also mark the extent of former glaciers.