In geology, a stock is an igneous intrusion that has a surface exposure of less than 100 square kilometres (40 sq mi), differing from batholiths only in being smaller. A stock has a discordant relationship with the rocks that it intrudes. Many stocks are cupolas of hidden batholiths. Some circular or elliptical stocks may be volcanic plugs, which fill the vents of now extinct volcanoes. A boss is a small stock.