The stone in this area is limestone, formed some 340 million years ago from soft, muddy, lime-rich sediments at the bottom of a warm tropical sea when this area was just south of the equator.
A collision between the tectonic plates caused these horizontal rock beds to fold up into great mountains. As the region moved north across the equator, the mountains were eroded away until the land was reduced to a flat surface.
Over millions of years, these soft beds became buried by further layers which, in turn, became compressed into hard rock.
Fossils show that the sea above these new rocks teemed with many types of fish, sharks and shellfish. Coal formed in layers or seams. Mining in this area of South Gloucestershire removed quantities of the coal.
With the age of industry brought the search for fuel. Drift mining began in this area, mining of the coal deposit by underground methods, or the working of coal seams accessed by adits (clefts into the rock) driven into the surface outcrop of the coal bed.
Drift is a general mining term, meaning a near-horizontal passageway in a mine, following the bed (of coal, for instance) or vein of ore. A drift may or may not intersect the ground surface and is the kind of mining done when the rock or mineral is on the side of a hill. A great example of what an adit is, is found here
To be able to log this earthcache you need to visit the co-ordinates. Nearby you will see the remains of the chimney and walls of the engine house for Webb's Heath.
The last working mine in Bristol closed it's doors in the 1960's. The coal found hereabouts was difficult to get at but was of sufficient quality to make the extraction worthwhile. The Webb's Heath mining was supposed to be extracted by digging via a shaft driven along underground but the shaft was in the wrong place and went in the wrong direction, so the pit was soon closed. The seam was mined towards the Crown colliery. Much of what was found was used in steam engines.
Email your answers to us before logging a find please.
Q1. Observe the area. North of here, what can be seen? The Drift mining carried out at Webb's Heath began in 1900. Explain, in your own words, how coal was extracted here.
Q2. In which direction do you think the seam was mined?
Q3. On returning to your parking co-ordinates , you should see large shallow indentations in the ground. Many of these have water in them. What do you think caused this?
A photo of you or your GPS at the chimney would be great to see.
Well done to The Kosciows for First to Find.