The square form green glass bottle was hand blown and has a deep punt unpolished pontil on the underside. The square form could be as early as the 1700's; however the threaded metal (possibly pewter) top with dolphin form stopper is later 19th century Victorian era. The fish does not necessarily look like a dolphin, however that is what they are called. It is possible that the topper was added later. Square form bottles would have generally been used to hold medicinal fluids. The estimate is based on actual recent past recorded auction sales of comparables. Retail 'asking prices' can be higher and vary.