What accounts for the springs that appear now and again on the Common (and in Norbury Grove) and which once upon a time led fashionable Londoners to visit Streatham to take the waters?
The answer lies in the geomorphology of the area. Streatham Common occupies a swathe of land at the western extremity of the Crystal Palace ridge, the focal watershed of South London. The upper Common, at its interface with the Rookery and Norwood Grove, attains heights between 75 and 85 metres above mean sea level; the lower Common falls away to a lowest point of 45 metres in the vicinity of Streatham High Road. Most of the lower and upper Common areas consist of London Clay, but the highest point – with adjoining areas of Norwood Grove – has a capping of “pebbly gravel and sand .. of uncertain origin”, according to the British Geological Survey.
This isolated capping at Streatham Common is exposed and easily identified along informal pathways through the wooded areas, where leaf mould has been worn away by walkers and the loosened soil has been washed away during heavy rain; indeed some of the paths have the appearance of having been artificially surfaced with the material!
The junction between the gravel capping and the underlying London Clay forms a spring line (an occurrence seen at other points around the Crystal Palace ridge, as at Sydenham) that gave rise to the historic spa industry in various localities.
Today, the spring line is visible in the form of an intermittent stream that flows down a ditch marking historic administrative boundaries. The streamlet in turn forms part of the Norbury Brook within the wider drainage system of the River Graveney, an element within the Wandle Basin.
Streatham Common’s variety of geological terrain and magnificent viewpoints across the Wandle and Graveney valleys combine to earn the site recognition as being one of the finest in London for the teaching of geography and geomorphology, acknowledged by the late Professor Wooldridge of King’s College London, who conducted field trips to the area and included it in his text book London’s Countryside. These views are interpreted on the Common’s Millennium panels.
It should be noted that the geological strata of the Common have been disturbed by engineering work undertaken for the construction of the South London Ring Main and for the widening of the A23, both of which programmes altered surfaces and gradients and disturbed drainage, exacerbated by less than sensitive works of reinstatement.