1. The term laterite is used in two ways, namely, stratigraphically as the name of a geological formation, and petrographically as the name of a tropical superficial rock. This discussion relates only to the use of the term as a rock name.2. Laterite (or rather some varieties of it) is formed by a process, the modus operandi of which is not discussed here, by which certain rocks undergo superficial decomposition, with the removal in solution of combined silica, lime, magnesia, soda, and potash, and with the residual accumulation, assisted, no doubt, by capillary action, metasomatic replacement, and segregative changes of a hydrated mixture of oxides of iron, aluminium, and titanium, with, more rarely, manganese. These oxides and hydroxides of iron, aluminium, titanium, and manganese are designated the lateritic constituents.3. This residual rock is true laterite, and the presence of any considerable proportion (> x10 per cent) of non-lateritic constituents requires expression in the mime, as it always indicates want of completion in the process of lateritization. True laterite contains, then, 90 to 100 per cent of lateritic constituents.