The Tangible Evidence from the Fremington Clays

 

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The famous red potter’s clay of Fremington in North Devon powered the Fishley and later Brannam potteries for generations. Its smooth, stoneless upper beds produced excellent throwing clay for slipware and sgraffito earthenware. What is remarkable, however, is that this same deposit was long interpreted as glacial till (boulder clay) laid down directly by a major Irish Sea ice sheet. Given that raw glacial till is typically a chaotic, gritty mixture full of stones and boulders — material that is almost useless for fine pottery — the traditional “till” label has always sat rather uneasily with the clay’s actual character.

Since George Maw first described the deposit in 1864 and called it boulder clay, many distinguished geologists — including Zeuner, Stephens in the 1960s–70s, and Kidson & Wood in 1974 — treated the Fremington Clay as key evidence of onshore Irish Sea glaciation during the Wolstonian (or even Anglian) Stage. A handful of far-travelled stones helped reinforce this view. Yet the finest pottery beds are remarkably pure, homogeneous, and free of coarse inclusions — features far more typical of quiet sedimentation than of ice dumping unsorted debris.

There is a far more convincing explanation: the Fremington Clay largely represents the remains of a shallow ice-dammed lake (glaciolacustrine deposits) formed when ice or ice-marginal gravels blocked the Taw valley near the coast. Fine silt and clay settled slowly out of suspension in these still waters. The very existence of such a lake actually helps define the limit of significant onshore advance by the Irish Sea ice rather than proving a thick ice sheet overrode the area. Occasional “touches” of marine diatoms (often abraded and derived) suggest the lake was sometimes linked to estuarine or marine waters, while the very rare ice-rafted erratics are best explained as dropstones released from floating icebergs — not material scraped along by a grounded glacier.

In this respect, Fremington fits a wider British pattern where quality is defined by water. While Britain’s other premier pottery clays—the ball clays of Devon and Dorset, the London Clay, and the Carboniferous fireclays—were deposited in river and lake systems millions of years before the Ice Age; the much younger Fremington beds owe their quality to a similar process of gentle water sorting. Whether ancient or relatively recent, these water-laid deposits left a plastic and almost stone-free material (unlike the Cornish china clay, which formed in situ within granite). This stands in stark contrast to raw glacial till, which remains too unsorted and stony to have ever served as a direct commercial source of high-quality throwing clay in the UK