Information Board: Brickmaking near the Viaduct
The pond beneath the Viaduct was partly created from the hole excavated for a brick
pit in 1860s-1880s. The Viaduct itself was built across the small tributary that
supplies the Hampstead branch of the River Fleet and was the beginning of Sir
Thomas Maryon Wilson’s proposed development at the top of the Heath. Happily he
was prevented from continuing with his project so instead he laid railway tracks on the road from South End Green and used these to exploit the clay for brickmaking.
London Clay, as the name suggests, underlies most of the London area. It was
deposited as mud on a marine shelf about 52 million years ago, supplied by rivers discharging from a coastline, probably in the Midlands. It is thought to have been
laid down under semi-tropical conditions similar to those in Malaysia and Indonesia
today although some seasonality has been deduced. As the London Clay basin filled
up the sediments became coarser and the alternating sands and clays at the top are known as the Claygate Beds. These sandy clays are particularly good for brickmaking and have been exploited all around the hill on which Hampstead Heath sits. Chalk and ash were imported up the hill to mix with the clay which was then moulded into bricks and fired on the spot in large ‘clamps’. The finished bricks were then transported back down the hill to South End Green. It is hard to imagine the foul smell of sulphur in this now pleasant spot.
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