An Encyclopaedia of Indian Archaeology v1.c14.s6.1

v1.c14.s6.1

The term laterite was coined by Buchanan in 1807 to describe a brick-like (Latin *later*, brick) geological formation in Kerala. The first palaeolith in India was discovered by Foote in a laterite gravel at PALLAVARAM near Madras in 1863 [4.2]. Subsequently the laterite has been studied as a source of economic minerals (iron, manganese, aluminium), as a product of tropical weathering, as an indicator of palaeoclimate and by archaeologists as an important tool-bearing formation. Indurated laterite which occurs widely in India, S.-E. Asia, Africa, Australia and s. America has been variously described as duricrust, ferricrete, plinthite, cuirasse and lateritic iron-stone. Unconsolidated lateritic soils have been classified as oxisols or latsols. In India 'lateritic' has been proposed for tool-bearing laterite gravels. Geologically primary laterite is a product of the sub-aerial weathering of ferruginous or aluminous rocks, e.g. basalt, granite, quartzite, limestone, even fluvial gravels, etc. Laterites are widely distributed in semihumid intertropical regions. Low relief where weathering exceeds the pace of surface erosion, seasonal rainfall of more than 1000 mm per annum, mild fluctuations in the water-table and evergreen or savanna vegetation favour laterite formation. Fossil laterites are found in arid and even temperate regions. The process of lateritization is slow, involving the leaching of bases, concentration of iron both by capillary action and lateral contribution from adjacent iron-rich weathering zones. A typical laterite profile comprises the crust overlying the mottled and pallid zone (lithomarge) with the weathered parent material at the base. Hydrated oxides of iron and alumina predominate in the crust and kaolinite in the lithomarge. Secondary laterites comprise reconsolidated debris from the older laterites, with or without material derived from other rocks. In India primary and secondary laterites occur both on high-level plateaux and coasts. Primary laterites date from the Cretaceous to the Early Pleistocene (?), while secondary (tool-bearing) valley and slope laterites are not older than the Middle Pleistocene [9.8.2]. Archaeologically remnant laterites on Tertiary erosional surfaces, pseudokarstic caves in indurated laterites and the older alluvial laterite gravels provide evidence for Late Pleistocene Palaeolithic [4.2] settlements, particularly in e., c., and s. India and parts of coastal Maharashtra. Fossil laterites underlying non-lateritized Middle-Upper Pleistocene tool-bearing gravels in the c. Narmada valley, n. Gujarat and the semi-arid zones of the Karnataka and Maharashtra plateaux are suggestive of a more humid palaeoclimate.