Louis and Mary spent all the time they could at Olduvai Gorge, starting in 1951. So far they had discovered only stone tools. A more extensive excavation came in 1952. They found what Louis termed an Oldowan "slaughter-house", an ancient bog where animals had been trapped and butchered. Louis was so carried away that he worked without his hat and his hair was bleached white from the sun. They stopped in 1953.