In 1841, James Ross discovered the Ross Sea, Victoria Land, and the volcanoes Mount Erebus and Mount Terror, which were named for the expedition's vessels. They sailed for along the edge of the low, flat-topped ice shelf they called variously the Barrier or the Great Ice Barrier, later named the Ross Ice Shelf in his honour. The following year, he attempted to penetrate south at about 55° W, and explored the eastern side of what is now known as James Ross Island, discovering and naming Snow Hill Island and Seymour Island.