Stylolites are structures usually found in limestone, and are made of silt. They begin as a flat layer of silt on top of sand or on a reef. If buried and enclosed by calcium carbonate, differential dissolution occurs and causes an unevenness to develop. Impressions of shells are also found at this site. In a slightly acidic situation, calcite is less susceptible to dissolution than aragonite.
Oysters have thick shells in order to resist being bored into.
However, oyster drills can penetrate their shells. At Hempstead Harbor, oyster drills are not found as fossils, but the oysters have drill holes in them. The oyster drills have been dissolved away. Oysters are filter feeders that create pseudofeces which is silt bound by mucus. Thus, they trap and bind sediment.