Gibsons Cave
Situated in the North Pennines’ Area of Outstanding Natural Beauty, Teesdale is home to some of the UK’s most impressive scenery and its most interesting geology. The Bowlees area is easy to access and nearby a convenient visitors centre complete with car park and toilets. This earthcache takes you on a short walk up the side of the valley to the waterfall known as “Gibson’s Cave”.
Teesdale is an excellent place to see a huge number of geological features, some of which cannot be seen anywhere else in the UK. This walk will allow you to see the variety of the sedimentary units within Teesdale in addition to how they can relate to one another.
Sedimentary rocks are those that have been formed by deposition of material, usually underwater. Over time this material, the general name for it being sediments, becomes compacted and eventually undergoes lithification – it turns from lots of small separate grains into a whole rock.
Different sedimentary rocks can often occur in repeating sequences. Repetitions of the same sequence can form a cycle. These cycles show sea level changes in the world where the rocks were deposited, and are referred to as Cyclothems. The rocks in the area around Bowlees are Carboniferous in age, lain down between 345 and 330 million years ago. At this time the area was not only underwater but also near the equator, and the North Pennines was periodically covered with tropical seas, river deltas, and large rainforests, depending on changes in the sea level. As a result, the rocks you will see are part of a cyclothem system showing Limestones, sandstones, mudstones and occasionally coals, which allow us to see this sea level change.
The Limestones in the area are well exposed in the Quarry just north of the car park for the Bowlees Visitor’s Centre at GR90732 28436. The sandstones and mudstones are better exposed at the end of the walk, up at Gibson’s Cave. As you walk up the river you will be able to see all of the rocks alternating as the erosion of the stream exposes them.
Gibsons cave at GR90958 28436 allows you to see a full cycle within the sequence. The base of the waterfall is limestone and was formed when the area was under relatively deep water. As sea level falls this changes into an alternating series of sandstones and mudstones, which were formed in shallower seas and river deltas and make up the middle of the “cave”. The top of the waterfall is another layer of limestone – this represents a sharp sea level rise that forced the area back under deeper water, and the start of a new cycle.
We hope you enjoy your visit to Teesdale and Bowlees and learn something about the local geology within the area. If you wish to discover more around the North Pennines then the visitor’s centre has many suggestions for other walks in the surrounding area.
Questions
Some of the rocks erode faster than the others and hence there are ledges within the stream – can you see which rock types are least resistant to erosion and generally is seen below ledges of the other, harder rocks?
Limestones are formed from the shells and bodies of sea-dwelling creatures. Sandstones and mudstones are different in both colour and texture, where do you think the sediments to form these rocks could have come from, considering they form in river deltas?
Using the board by the quarry near the start of the path up to the cave, take note of how long ago the quarry stopped being a working one. Why do you think it is no longer active?
Published with the Permission of North Pennines AONB Partnership