Q. Can you get from Hampstead to the River Ganges via a London Stock Brick and back again in five moves?
A. well, perhaps… at a push…
1. Hampstead: Hampstead stands on one of the highest hills in London, its summit – a sandy ridge 443 feet above the sea-level – rests on a belt of sandy clay which protrudes at the edges and is underlain by water-resistant London Clay.
Rainwater penetrates the sandy upper layers only to be forced out again by the impermeable lower London Clay, creating a landscape of rolling well-drained ‘upland’ heath (which easily dries out) and swampy hollows where feeder streams flow towards the hidden rivers of the Fleet and Westbourne which in turn pipe into the River Thames.
2. From Hampstead to the Claygate Beds: London Clay underlies most of the London area. It was deposited as mud on a marine shelf about 52 million years ago. It is thought to have been laid down under semi-tropical conditions similar to those in Malaysia and Indonesia today. As the London Clay basin filled up, the sediments became coarser and the alternating sands and clays near the top are known as the Claygate Beds. The Claygate Beds and Bagshot Beds are the uppermost geological formations of Eocene age (56 to 33.9 million years ago). The Claygate Beds consist primarily of course silts and clays with sand, whilst the Bagshot Beds are predominantly finer grained sand.
3. From Claygate Beds to the Ganges: The Claygate Bed were formed by displaced sediment carried by a huge and ancient river. The Great Bagshot River laid down material gathered from Salisbury Plain, through Bagshot, reaching North London before flowing into an early North Sea. Some levels are peppered with seams of pebbles. All are flint pebbles, weathered out from the chalk of the Wessex Downs, rounded as a result of being swept along by the powerful currents of the Great River flowing from SW England, across the Salisbury Plain, to deposit thick river sands in the London Basin. The lines of pebbles record periods of flood when the river had more potential to carry larger particles. The River was immense similar in length, size and potency as the Ganges today
4. From the Great Bagshot River to brick clamps: The silts and clays of the Claygate Beds together make an excellent blend of materials for brick-making. When fresh and unweathered, London Clay is rich in iron pyrites (sulfide) which changes to sulfate on exposure to air. Sulfate takes the form of crystals of gypsum (calcium sulfate) — liable to cause bricks to burst when they are fired in a kiln.
On the Heath, the clay was dug by hand, and cut from terraces notching the hillside. It was then left exposed to the rain to flush out the gypsum. Finally it could be blended with the fine silts of the Claygate Beds, together with the ‘brick earth’ (wind blown silt from the top of the Heath).
Many of the bricks were fired in very simple kilns. If the wind was in the East, the reek of sulfur smoke must have hung heavily over Hampstead. The product was a yellowish stock brick. The outer bricks of the kiln often fused together to form distorted blocks with glazed surfaces which can be seen in garden walls throughout Hampstead.
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. The term ‘stock brick’ indicate a common type of brick stocked in a locality. The stock brick is an unlikely London icon:
“…it is unassuming, unrefined, pock-marked and crinkled like aged skin. Its surface is mottled, with earthy hues daubed grey or black by the smog of industrial London. Because of its handmade quality the contours of each brick are irregular, and no two are the same. This ubiquitous object is the physical residue of a London era, testament to the fire, mud and human sweat that forged the stock-brick landscape of Georgian London.”
5. Brick Clamps to Brick Fields and Hampstead Viaduct
The pond beneath the Viaduct was partly created from the hole excavated for a brick pit in 1860s-1880s. The Viaduct itself wasn’t built to span the pond, there was no pond, just a marshy hollow through which ran a piddling small tributary supplying the Hampstead branch of the River Fleet. Much more the Viaduct was a symbol of 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 exposed Claygate Beds for brick making.
Between 1866 and the end of the century, there was an extensive brickfield on the West side of the Heath, stretching from The Viaduct down the valley of the Hampstead Ponds. It was an despoiling enterprise generated by a thwarted Sir Thomas Maryon Wilson allowing John Culverhouse, a local builder, to make the bricks needed for the extended terraces of the expanding village of Hampstead.