When Navy divers and NOAA National Marine Sanctuary marine archaeologists recovered the USS Monitor steam engine from the Atlantic in 2001, the pioneering Civil War propulsion unit was covered in a thick layer of marine concretion. Sand, mud and corrosion combined with minerals in the deep Cape Hatteras, N.C., waters to cloak every feature of Swedish-American inventor John Ericsson's ingenious machine, and they continued to envelop the 30-ton artifact after nine years of desalination treatment.
http://www.youtube.com/watch?v=M_8b_gWuOYk