Discovery and research While travelling in German East Africa in 1911 to investigate sleeping sickness, German physician and archaeologist Wilhelm Kattwinkel visited Olduvai Gorge, where he observed many fossil bones of an extinct three-toed horse. Inspired by Kattwinkel's discovery, German geologist Hans Reck led a team to Olduvai in 1913. There, he found hominin remains which were later radiocarbon dated to 17,000 BP. Four more expeditions were planned, but World War I prevented their start. After the war, as Tanganyika came under British control, Louis Leakey visited Reck in Berlin and viewed the Olduvai fossils. Louis Leakey became convinced that Olduvai Gorge held stone tools, thinking the deposits were of similar age to the Kariandusi prehistoric site in Kenya. Reck and the paleontologist Donald McInnes accompanied Louis Leakey in his 1931 expedition, where Louis found a number of hand axes close to camp soon after their arrival. Mary Leakey first visited the area in 1935, joining Louis and Percy Edward Kent. Subsequent visits were made by the Leakeys in 1941, 1953, 1955 and 1957. Louis and Mary Leakey are responsible for most of the excavations and discoveries of the hominin fossils in Olduvai Gorge. In July 1959, at the FLK site (the initials of the person who discovered it Frida Leakey, and K for korongo, the Swahili language word for gully), Mary Leakey found the skull of Zinjanthropus or Australopithecus boisei. In addition to an abundance of faunal remains the Leakeys found stone tools Mary classified as Oldowan. In May 1960, at the FLK North-North site, the Leakeys' son Jonathan found the mandible that proved to be the type specimen for Homo habilis. Archaeology and geology Hans Reck and Richard Hay While Hans Reck was the first geologist to attempt to understand the geology of the gorge, current understanding of the geology of the stratigraphic sequence of Olduvai Gorge was made possible in large part by the efforts of geologist Richard Hay. Hay spent twelve years studying the geology at Olduvai, much of it working along with Mary Leakey, finally formulating a detailed picture of the geologic history of the area. Hay's seminal work The Geology of the Olduvai Gorge was published in 1976. Reck identified five main layers of deposition in the gorge, which were labelled Beds I through V, with Bed I being the oldest and lowest in the sequence. Hay and other geologists working at the gorge