and composed of clays, and stream deposited sandstones and conglomerates. Four distinct tool-bearing levels are evident, including 500 handaxes and cleavers at the HK (Hopwood's Korongo) site, while phonolite handaxes and an elephant bone handaxe were found at the HEB (Heberer's Gully) site. The WK (Wayland's Korongo) site contained a Homo erectus pelvis and femur. Masek beds The Masek Beds are composed of two episodes of aeolian ash from Kerimasi. A number of quartzite handaxes were found in this layer at the FLK site. Dunes formed after the deposition of Oldonyo Lengai tuffs make up the upper portion of the Ndutu Beds, but yield few fossils. Oldonyo Lengai tuffs also make up the Naisiusiu Beds. Associated fossil species The few Australopithecus boisei remains, which include the skull, a thigh bone fragment, and several teeth, were found distributed throughout Beds I and II, which dates them in the range 1.1 to 2 mya. The more common remains of Homo habilis were found in Bed I and the lower portion of Bed II, which makes them contemporaries of Australopithecus boisei. Homo erectus remains were found in the upper portions of Bed II, making them contemporaries of Australopithecus boisei, but not of Homo habilis. The stone tools and their makers Louis Leakey first described the Oldowan stone tool industry in 1951. The Leakeys determined that choppers were the most common stone tool found at the gorge, amounting to over half of the total number, and identified 11 Oldowan sites in the gorge, 9 in Bed I, and 2 in Bed II. They also identified the Developed Oldowan as the subsequent diverse tool-kit found in Beds II, III, and IV, with small tools made mostly from chert rather than quartzite. These tools are mostly spheroids and sub-spheroids, followed by choppers. Besides the chert quarry in Bed II, the Leakeys were able to identify the other source locations of the principal rocks used to make the stone tools. The most common material was quartzite, which originated from the Naibor Soit Inselberg just north of the gorges. The phonolite originated from the Engelosen volcano 5 km to the north. The gneiss came from the Kelogi inselborg 9 km to the southwest. The first species found by the Leakeys, Zinjanthropus boisei or Australopithecus boisei (renamed and still debated as Paranthropus boisei), featured a sagittal crest and large molars. These attributes suggested the species engaged in heavy chewing,