Sailing east they reached a 200-foot ice cliff which they called the Great Southern Barrier, now the Ross Ice Shelf, and followed it so reaching 78°4'S. By depth sounding adjacent to the ice they determined the ice was floating and was therefore 1000 feet thick. At a low point in the ice cliffs they could see from the masthead an enormous plain of frosted silver and they were certain there was no open sea further south. After following the barrier for over 250 miles and with the Antarctic winter approaching they returned to the west but, near Mount Erebus, could not get ashore. They were 160 miles from the south magnetic pole - 700 miles nearer than anyone had been before. After passing Cape Adare, they again succeeded in breaking through the pack ice and reached Tasmania on 6 April 1841 to be greeted by John Franklin and crowds of well-wishers. As it happens Erebus and Terror were the last vessels to navigate the Ross Sea using only sail.