Although we use the magnetometer and the multibeam echosounder, we do in the end need to get our hands on some of the rocks from the ocean floor. We do this in a truly ancient way, using a steel dredge dragged behind the ship. The dredge has a big wire basket for collecting the rocks and is pulled by a strong wire cable that leads up to the ship. The water is usually 1 to 3 miles deep and the rocks usually rough and strong. We need to get the dredge in the right place, drag it along slowly, pull hard enough to break off some rock and then bring it back up to the ship. It may be bulging full, or may contain just a few cobbles (of great interest) or may be empty. Usually somewhere in between.