Wilman. Gerhard and Dora Fock followed up Wilman's work in the 1960s-1970s, documenting in detail the engravings at the major sites of Bushman's Fountain, Kinderdam and Driekops Eiland, and at several hundred other locales in the Northern Cape and adjoining districts. When G. and D. Fock documented Wildebeest Kuil in 1968, they recorded 178 individual engravings. Detailed mapping has since revealed more than 400 engravings. Engraving technique Most of the engravings in the Kimberley area are made with the 'pecked' technique: a hard stone was used to chip away the outer crust of the rock, exposing the lighter coloured rock beneath. Sites north west of Kimberley are often on andesite outcrops (as at Wildebeest Kuil and Driekopseiland) while to the south, in Karoo geological settings, the koppies are mostly dolerite. With time, the exposed portions of the older engravings have become as dark as the outer crust through the build-up of patina. The age of the engravings The pecked engravings of the area are estimated to span a period from perhaps a few hundred to possibly several thousand years ago. Direct cation ratio dating methods applied at Klipfontein, giving estimates spanning the entire Holocene, hinge, however, on a calibration curve of uncertain reliability, and the samples were too small to run more than one assay each. Hairline engravings, known from a few sites in this area and more commonly in the Karoo, are consistently beneath pecked engravings in superimposed sequences, and are thus older. Butzer used geomorphological evidence to infer bracketing ages for the engravings at Bushmans Fountain and Driekopseiland, with the resulting scenario being in broad accord with more recent work on palaeoenvironmental change at a regional scale, as well as with findings at other sites, and observations of associated archaeological material. At Wildebeest Kuil some of the engravings were undoubtedly made by Later Stone Age occupants of the site 1200–1800 years ago, as suggested by the radiocarbon readings cited below. Interpreting the engravings Given a shamanistic understanding of the art, the Wildebeest Kuil engravings may well relate to beliefs about the rain and rain-making. Medicine people or shamans could access the spirit world through altered states of consciousness and harness supernatural power to heal the sick, control animals, and make rain. It is possible that many of the engravings were inspired by visions experienced in altered states of consciousness, and depicted on the rocks so that others could