Geology at High Elms

Paul Rainey crumbling a piece of Seaford Chalk

Wherever I have lived, if there has been a garden the soil has seemed mostly to consist of clay. I had a vague image of the earth as consisting of rock, with clay on top. Even though I knew quite well that there were many other sorts of environment, in practice it always came back to clay.

Much of my current locality is chalk or gravel. How does this affect my current garden? Not at all, because the house was built on an old railway yard, and if I dig down a foot through the clay I find coke.

On Sunday there was a geology walk around High Elms Country Park and its immediate neighbourhood towards Farnborough, led by Paul Rainey of the Ravensbourne Geological Society. This area is almost all on chalk. You can see chalk very close to the surface; nearby, I have seen it turfed out of a badger's sett, and here it can be seen in road cuttings.

There is another way to see what is near the surface in woodlands in the south of England. All the woods have many trees that were toppled during the Great Storm of 1987, when winds of hurricane strength blew down an estimated 15 million trees. I got that number from Wikipedia, but I remember that night well. When those trees were pushed over, their root balls were tilted up and they brought with them all the attached soil. That soil is still mostly there and gives you a very good idea of what's under the topsoil, without having to dig.

Flint Lodge, the gatehouse to High Elms, showing flint in the walls

The top photo shows Paul Rainey crumbling a piece of chalk from one such root ball. Like all experts, Paul could read more from his surroundings than those less knowledgeable. Chalk, being a rock, albeit a weak one, can support more of a slope than clay or gravel. We were on Seaford chalk, and elsewhere on the estate is a layer of Lewes chalk, which is stronger and supports steeper slopes.

Chalk, of course, is full of flints. The Blackheath gravel layer of the nearby Hayes, Keston and West Wickham commons consists of small black flint pebbles, created where a sea has broken up larger flints and rolled them around. There were many such pebbles on the surface as we walked, which must have come downhill from elsewhere, as there is no gravel layer here.

Flints were a valuable resource in the stone age, and in more recent times they were used to surface walls, for protection or decoration. The area is full of houses and churches that demonstrate this. The second photo shows Flint Lodge, the gatehouse of the High Elms estate, which demonstrates this in name and in fact. The white border around the broken edges shows that these flints were freshly dig for this use. That border is usually weathered off on flints taken from the surface.

A chalk pit in High Elms Country Park

At the top of the slope is a playing field attached to Farnborough Village. Here, there is a layer of Thanet sand. Sand, chalk, flint, gravel .. it's easy to see that this whole area was once a sea-bed.

The various soils and rocks in this area have in the past been used as resources by the locals. The playing fields at Farnborough were once a sand pit. The gravel at Keston Common was a local resource. And here in High Elms Country Park is a chalk pit.

It goes down about 30 feet and branches out into three short excavations. This is where chalk was excavated to put on the fields, though just why the fields weren't already chalky enough I do not know. Chalk was taken from deep down because that nearer the surface was only good for paths and roads, not for the fields. This pit is now a home to bats; I wasn't able to find out what type.

(Added later: I have since heard from Ishpi Blatchey, a local bat expert, who wrote: "The ... dene hole .. is a bat hibernation site - not used in the summer as it is too cold for maternity roosts. Brown long eared, Daubenton's, and Natterer's bats are regularly seen there in winter by licensed bat workers who monitor the site for the National Bat Monitoring Programme." Here is a note of one of Ishpi's bat walks.)

As you can see, it rained during this walk ...

Here are some random images.

Cut ivy stems on a felled treetrunk near High Elms

Ivy can be quite substantial, and can be considered as a workable wood in itself.

Last Autumn's fallen leaves with signs of tar spot fungus

The edge of the field was full of leaves like this.

Weathered gate ball at The Clock House, High Elms

This was one of the decorative balls on the gateposts of The Clock House. I don't think it will last much longer. One good frost should split it apart. In fact, I can't see how it is still holding together.