As you approach the cliff from a distance it just looks like it has a clean cut hole in the rock or an old cave, however as you get closer to it it becomes clear that is not the case
When you get near you can clearly see the cliff face isn't just one sheer face of flat rock, it is made up of lots and lots of layers of rock one on top of the other, the rocks in the layering here are not the same sort either throughout, which is a clue to why this feature is here, what are the rocks and how did this place come to be ?
Geology
The layers you will now be looking at in and around the cave are formed of limestone and shale. The Limestone is a grey/brown colour with veined sections, it is known as "Penmon marble", Brachiopod fossils are sometimes found in it. Shale is a fine-grained, clastic sedimentary rock composed of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite.
The cliff here has been moved many times due to faults fracturing and moving the beds of rock (layers), and there are distinct lines where the beds have been moved
(if you go to the following coordinates you will see a huge bed of shifted limestone, you can actually climb up onto it and inspect the area: 53.18.716 004.02.788)
The cliff is itself is approximately 25 feet high from the ground; if you now have a look at the layers you will see that the distribution of the limestone and shale previously mentioned is not equal, near the top and bottom of the cliff. There is a gradual change of shale to limestone; near the bottom there is a lot more shale per metre of rock and nearer the top there is a lot more limestone. The cliff has been struck by several faults, causing it to look unstable; in fact if you walk through the cave to the other side you will see the ground around you or 'beds' are at an angle, the beds are angled due to folding, which has caused the rock to tilt, this in turn can dislodge rocks in the cliff and cause them to fall
Coastal Erosion and cave formation
The faults and folding are not the sole cause of the cave formation however, Penmon, as you will have noticed is very close to the sea, this makes it prone to erosion as the sea waves lap against the bare rock without any form of barrier or protection. As mentioned above if you look at the cave right at the bottom you will see there is a much larger portion of shale than limestone, shale is eroded at a far quicker rate than limestone and because it is present in a large quantity at the bottom of the cliff where the sea washes against it, it has eroded away and caused the thinner beds of limestone between the other shale layers to collapse causing the arch to form under the cliff. If for instance there was a far higher portion of shale than limstone the chances are this would not be a cave it would simply be a pile of limestone where it had collapsed totally due to its instability. Where there are less shale beds. Faults passing through the cliff have displaced the beds, one such fault almost 23 cm, causing a ledge halfway through the cave
To log this Earthcache please complete the following tasks at the site
1. Take a photograph of the shale layer
2.Take a photograph of the limestone layer
3.Take a photograph of the uneven rock beds caused by folds near the second set of coordinates
4.take a photo of the large fallen rocks at the cave entrance caused by faults and folding
5. Get a picture of you or your GPS inside the cave and EMAIL me an estimate of how high / wide it is.
Any logs without required photo's will de deleted
* At the second set of coordinates (53.18.716 / 004.02.788) you can walk pretty much down to the sea along the large limestone ledge and back along the opposite side, there are some very unusual rock shapes features to be seen, although it's not a logging requirement for the earthcache if you do take any pictures I would be enjoy having at look at them posted in the logs.
Enjoy !
PLEASE NOTE: I receive a very high number of Earthcache emails, I can’t reply to them all otherwise I’d be doing nothing else all day, as has always been the case there is no need to await a reply from me regarding your answers…. However due to numerous people thinking they can just log these caches without emailing any answers, and/or completing the required tasks these will be picked up, and the logs will be deleted without further communication. To facilitate this Please email your information either before, or AT THE SAME TIME OF LOGGING THE CACHE, Thanks.