Abstract The Quaternary, or final period of geological time, has been popularly equated for the last 150 years with the ‘ice age’, when glaciers invaded many high latitude and high altitude parts of the Earth’s surface not previously glaciated since at least the Permo-Carboniferous. Early in the 19th century a distinction was drawn between the ‘solid’ rock formations, which often show a regular stratigraphic order and uniform thickness because of deposition in extensive marine basins, and the thinner, unconsolidated and much more variable ‘drift’ or superficial formations now known to result from more recent deposition mainly in glacial and other non-marine environments. The terms solid and drift are still preserved in the legends of quite recently published British Geological Survey (BGS) maps, although since 2004 they have been replaced by ‘Bedrock’ and ‘Superficial Deposits’, respectively. Over most of England and Wales they correspond to pre-Quaternary and Quaternary deposits. The term drift (or diluvium) originally implied deposition by waters of the Biblical Flood, but with increasing exploration of polar regions in the 19th century it became popular to invoke floating ice as a depositional agent, accounting especially for the large blocks of identifiable rock types (erratics) displaced long distances from their nearest known outcrops. However, both flood and floating ice implied an unlikely submergence of great depth in order to deposit erratics and other drifts on mountains well above present sea level, for example on Moel Tryfan in North Wales, where Quaternary marine molluscs occur at 430 m OD.