One Tree Hill is a section of Langdon Hills Country Park that is managed by the rangers from Thurrock Council but straddles both Thurrock and Basildon.
Geology
The rock types found in this area consist of London Clay as the base, with Claygate Beds and Bagshot Sand on top of this. There is then an additional layer of flint gravel on top, referred to as Stanmore Gravel on geological maps.
The lower three levels of the geology were formed on the floor of a sub-tropical sea about 50 million years ago when the UK was in a warmer location due to continental drift. The flint, however, is from a more recent deposition and is thought to be fluvial (river based) in nature. This is possibly surprising when you think that you are on one of the highest areas of land nearby. It is believed that the River Thames flowed across North Essex and Suffolk prior to the last Ice Age and it was a tributary flowing from Kent towards the Thames that deposited the flint. This flint then protected the hills whilst the surrounding area without this harder top were eroded. The Thames is believed to have moved to its current course about 450,000 years ago.
For more information on the Geology of the area visit http://www.essexfieldclub.org.uk
Erosion
There are many sorts of erosion, however, as mentioned earlier the area has been affected by both fluvial and glacial erosion. Fluvial (river based) erosion results in smoother rocks being formed, whereas glacial erosion results in a mix, but often with much more angular material.
The views
If you walk towards the trig point and stand on the steps you get a superb view of the River Thames and its floodplain.
As you look to the South you are currently stood on a bluff and can see the last meander (bend) of the River Thames before it hits the Estuary and the North Sea by Southend. You can also get an idea of the number of properties at risk from future sea level rise due to their location on the flood plain of the River Thames.
You are in the lower course of the river and therefore can see the kind of features in the diagram above.
Meanders are formed by a combination of erosion (on the outside of the bend) and deposition (on the inside). If you can imagine a circular running track with the runners all starting in a straight line and holding hands. For them to all keep in a perfectly straight line the outside runner has to run a lot faster than the inside runner as they have to cover a greater distance. For this same reason the outside of the meander has to flow faster and this causes erosion to take place. Whereas on the inside the river is flowing more slowly and therefore deposition takes place.
The floodplain that you can see has been built up through many floods depositing layers of mud and silt leaving behind the clay geology common in the area.
Claiming the cache
To claim the cache please email me the answers to the following questions through my profile.
1) a)Describe the shape of the rocks in the side of the trig point at the coordinates and say what you think eroded them.
1) b)What type of rock is stuck in the side of the trig point at the coordinates given?
2) How many metal circles are on the top of the trig point?
3) If you walk down the steps to the south of the trig point to get a better view, describe 2 of the 3 fluvial landforms that you can see in front of you.
Hope you enjoy the views. There are several other caches nearby if you have the time to get them and to enjoy the woods.