An Exploration of Keston Common

 

A detail of the Blackheath Member of the Harwich Formation

Leaving the Church of St. John the Baptist in West Wickham, where I encountered a variety of building stones that I was not familiar with, I made my way along various public footpaths, which are underlain by the Chalk, until I reached a gentle escarpment that is capped by the Eocene Harwich Formation. 

 

An escarpment capped by the Harwich Formation

Although these are not mapped, the path traversed a sandy soil that is full of very rounded flint pebbles, which are presumably the remnants of sediments that were deposited on the Chalk and, when walking along the path up the escarpment, in a couple of places I noticed exposures that looked very similar to this. 

 

An exposure next to the public footpath

Reaching Heathfield Road, which runs along the edge of the escarpment, I turned south and after 100 metres I encountered the Keston war memorial, which is set in front of a semi-circular hedge with yew trees to each side of it. It was built in 1920 using Portland limestone to the design of the sculptor Sydney March and consists of a monolithic stone pillar buttressed on all four sides with a cruciform top, which has a very unusual form. 

 

Keston war memorial

Continuing down to the junction with Westerham Road, I went in search of the Keston Common gravel pit, which worked the Blackheath Member of the Harwich Formation – interpreted as the deposits of tidal channels and nearshore sand and gravel bars.

 

An exposure of the Harwich Formation

 

It mainly comprises small rounded black flint pebbles, which is in places well cemented and forms a solid rock section that is several metres high. I had never encountered rocks of this type or age before and I was therefore very keen to obtain a specimen for my growing rock collection. 

 

An exposure of the Harwich Formation

Not having my Estwing hammer with me, I looked around for a sturdy piece of wood to try and prise a piece off one of the exposures but, with this not being able to do the job, I instead used a large lump of solid gravel to break off a piece that I could carry home in my rucksack. 

 

A specimen of the Harwich Formation

Although it was not that easy to remove my sample, it has proved to be quite friable and, when transporting it back to Treeton in my suitcase with other well wrapped specimens, many fingernail sized pebbles became dislodged. The Harwich Formation at Keston Common has been described as being cemented with calcite in places but, when the dark brown cement in my sample was tested with hydrochloric acid, there was no reaction. 

 

The Harwich Formation

The pit was opened up to provide gravel for the repair and maintenance of the Westerham Road and other roads in the area. Its dimensions can be quite clearly seen on a LIDAR map, which is approximately 225 metres long and, at is maximum extent, 60 metres wide. 

 

A general view of the gravel pit

Heading north-east towards the Keston Common car park, there are further extensive exposures on the south side of the gravel pit, but I did not collect further samples and was just content to take a few record photographs before exploring the rest of the common. 

A view along the gravel pit

The River Ravensbourne rises from a spring at the junction of clay beneath the sands and gravels of the Harwich Formation, which has been engineered in brick and is called Caesar’s Well - a reference to a legend that Julius Caesar noticed a raven drinking here, when his legions were in great need of water. Certainly, the cold water here was since considered to have great medicinal value and was also very popular for bathing. 

 

Caesar's Well

I didn’t spend much time at the Keston Ponds and didn’t go to look for Keston Bog, which was studied by Charles Darwin, but instead had a quick wander around the common to see if I could see any evidence of the Iron Age embankment and ditch. The common is densely vegetated, which makes landscape features difficult to see, but a linear gorse covered feature, which rises slightly above the heather covered surroundings, is probably a section of this. 

 

A gorse covered Iron Age embankment

Numerous unmarked paths criss-cross the common and I just wandered around until I found one of the principal paths, which sometimes exposed pebbly beds of the Harwich Formation, before heading north to Fishponds Road. Carrying on to Keston village, I stopped at the Greyhound for a quick pint of beer before taking a few photos for the British Listed Buildings website, while walking back to Hayes. 

 

The Harwich Formation exposed in a footpath