The nature and origin of the carbonaceous matter ('carbon') in the gold-bearing reefs of the Archaean Witwatersrand basin of South Africa has long been a subject of controversy and debate. The importance of the carbon results from its direct association with the gold grade. The studies reported here were directed at resolving the nature and origin of carbon. Techniques used include stope-scale (macroscopic) mapping, mesoscopic (hand specimen) examination, and microscopic studies incorporating the use of optical reflectance measurement. Macroscopic mapping has demonstrated the braided habit of carbon bodies over tens of square metres, with a close parallel to sedimentology. Mesoscopic observations, however, show the vein-like carbon seams are often cross-cutting sedimentary features, with the carbon occupying an anastomosing set of bed-parallel fractures. Microscopic observations show a globular form for the carbon and inclusions of uraninite particles. In seam carbon the globules are generally modified into elongated 'spindles' oriented perpendicular to bedding. Optical properties are dominated by generally high reflectance and anisotropy with a 'swirling' liquid crystal structure, classifying seam carbon as 'carbonaceous mesophase'. It is this fine mesophase texture that has previously been wrongly attributed to plant (algal) morphology. Highly significantly, the optical anisotropy is bed perpendicular (rather than bed parallel as in normal sedimentary burial) indicating mesophase formation during fracture opening.Both reflectance and bireflectance of the seam mesophase show a range of values at all scales. No stratigraphic or depth trends were apparent, though geographic variation points to localization of the maximum temperature event(s). Given high anisotropies, maximum reflectance values in the 4-8% R o range and minima in the 1-2% R o range give arithmetic mean reflectance values of about 4.0% R o . Kinetic modelling equates these values with short term (50 000 years) temperature events of c. 400 C or burial temperatures of c. 280 C. Lower reflectance values of c. 2.0% R o obtained from the shales suggests thermal detachment of permeable and impermeable beds, a characteristic of pulsed hydrothermal flux. The included uraninite grains influence the orientation of the surrounding anisotropic mesophase demonstrating that uraninite predated the mesophase formation event. Regional palaeo-stress 'frozen' into the mesophase anisotropy indicates a NW-SE deviatoric stress.The combination of hydrocarbon, radiation and hydrothermal fluid flow marks Witwatersrand Basin pyrobitumens out as being different from conventional oil. Putative source rocks for the oil are identified in the intra-basinal Witwatersrand shale units. Lithological control in carbon seams is explained by the poro-perm and mechanical properties of the unconformity sequence of footwall, reef conglomerates and hanging wall quartzites favouring fracture along the unconformity surfaces. An overpressured oxidizing fluid created the fracture network that h...

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HE credit for the discovery of the great antiquity of Jericho belongs to Professor John Garstang, who excavated there between 1930 and 1936. In those days our T picture of man's emergence from Palaeolithic and Mesolithic savagery through Neolithic barbarism to the civilization of the metal ages was a neat and tidy one. The nomadic hunters of the first stage discovered agriculture and stock-breeding and were thus assured of enough subsistence to become settled villagers, self-sufficient and unprogressive, but at least no longer savages. After long years of this unprogressiveness the eventual discovery of the uses of metal led to trade, specialization, the need for surplus food to feed the traders and specialists, the growth in importance of favoured areas such as the great river valleys and the development of the villages there into towns through the accumulation of surpluses and the consequent need for organized rule to control them. The theory was reasonable, and what was then known about the early village settlements in Western Asia and the rise of towns and states in the river valleys of Egypt and Mesopotamia seemed to fit the facts. A chronology of early villages in the later fifth millennium and the growth of towns in the later fourth, leading to states in the third, seemed to cover what was known.Professor Garstang in his first soundings in 1935 of the lower levels at Jericho produced the first bit of evidence which was disturbing to the scheme. The Neolithic villages were characterized by the first use of pottery, the first of the new domestic arts and crafts, which were of obvious convenience to the housewife, but equally obviously an encumbrance to the nomad. The first pottery became in fact to many archaeologists the type-fossil of the Neolithic in place of the polished stone axes of the earlier generation. Professor Garstang's revolution was that at Jericho there was a perfectly good settlement over a long period of time, but no pottery.Starting from the point at which Professor Garstang's excavations were suspended, the present expedition has proceeded far in the elucidation of the Neolithic of Jericho, and has continued its predecessor's revolutionary career.We can in the first place claim that Professor Garstang's pre-pottery Neolithic people lived not in a village but a town. His discovery came late in his campaign, and he only located the typical remains in one spot, at the north-east end of the tell. With the advantage of the knowledge of what he had found, we could proceed to look for the same type of occupation elsewhere, and we have found that it extends beneath the whole eight acres of the Bronze Age city-no inconsiderable area by Palestinian standards, though not comparable with some of the great sites of Mesopotamia. We still lack accurate data about the Neolithic settlement to make a reliable estimate of population, but a modern oriental town of this size might house some three thousand people.Up to twenty successive house-layers have now been excavated in several different areas and, thro...

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