The thickness of glacier overpasses the local solid bedrock altitude When the glacier is climbing forward , causes the bedrock be subjected to abrasion and erosion in glacier forming isolated bulges , which reminds a sheep back. The side facing ice usually low and polished often with ice gliding streaks , while back side crashed by glacier , steep and star-like. The rock bulge is called sheep-back stone. Grog stone by Poyang Lake is this type.