St. Ninian's Cave EarthCache

Tradition holds that St Ninian’s Cave was the hermitage of its eponymous saint. This can’t be verified, but it may well have functioned as a retreat from the monastery at Whithorn. Ten crosses are cut into the cave wall itself, and 18 early Christian carved stones have been found in the cave. Geologically, the cave is a good example of the erosive forces of the sea however the cave today is a lot smaller than it once was, due to successive rock falls.

The Catholic Church described St. Ninian as a man from south west Scotland "who first brought the Christian faith" to the country around 397AD, when he is said to have established a religious community at Whithorn in Galloway. He then was said to have studied in Rome before being ordained a bishop. His monastery in the south of Scotland was known as Candida Casa, from the Latin meaning "White House". The name possibly refers to the stone used to construct it or the whitewash used to paint it, and has survived as the modern name, Whithorn. The precise details of these facts are disputed.

The cave should be accessible at all times but access might be harder at high tide as you approach along the beach. Extremely high tides or storms would be times to consider avoiding a visit. Please be aware that the cave and surrounding coastline is designated as an SSSI and therefore I am asked to remind you that it is an offense to intentionally interfere with the flora, fauna, or geological or physiographical features here and you do not need to touch anything in order to complete this EarthCache. The cave features in the final scenes of the Wicker Man film.

A sea cave, is a type of cave formed primarily by the wave action of the sea. The primary process involved is erosion. Sea caves are found throughout the world, actively forming along present coastlines and as relict sea caves on former coastlines. 

Sea caves may be found in a wide variety of host rocks, ranging from sedimentary to metamorphic to igneous, but caves in the latter tend to be larger due to the greater strength of the host rock.

In order to form a sea cave, the host rock must first contain a weak zone. The sea has taken advantage of this vulnerability and eroded away the weak zone to form the cave. The driving force in sea cave development is wave action. Erosion is ongoing anywhere that waves batter rocky coasts, but where sea cliffs contain zones of weakness, rock is removed at a greater rate along these zones.

As the sea reaches into the fissures thus formed, they begin to widen and deepen due to the tremendous force exerted within a confined space, not only by direct action of the surf and any rock particles that it bears, but also by compression of air within. Blowholes (partially submerged caves that eject large sprays of sea water as waves retreat and allow rapid re-expansion of air compressed within) attest to this process.

Adding to the hydraulic power of the waves is the abrasive force of suspended sand and rock. Most sea-cave walls are irregular and chunky, reflecting an erosional process where the rock is fractured piece by piece. However, some caves have portions where the walls are rounded and smoothed, typically floored with cobbles, and result from the swirling motion of these cobbles in the surf zone.

Weathering and erosion is responsible for the creation of a variety of coastal features, they include caves, arches, stacks and stumps 

• Caves occur when waves force their way into cracks in the cliff face. The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action is the predominant process.
• If the cave is formed in a headland, it may eventually break through to the other side forming an arch.
• The arch will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
• The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.
• Alternatively, changes in the cliffs and coastal erosion may cause cliff collapse near or at the cave which may actually cause it to shrink in size..

The rock here is graywackle sandstone. Inside and around the cave the varied colours must certainly be considered an important part of the charm of the place. Sandstone can become coloured in different ways depending on a variety of factors. These are some of the colours you might see here.

White / light grey

Freshy cut sandstone is often a bluey grey colour or quite a pale white when first quarried/eroded. This could then later change to one of the other colours listed below when it has been exposed to the environment for a while - but this isn't always the case, the stone may retain it's original colour as it depends on the ingredients found within the stone. Once the stone is cut open it becomes exposed to the oxidants produced by oxygen and water and they could react with the stone and cause the colour to change.

Yellow / tan

The most common cementing materials in sandstone are silica and calcium carbonate, which are often derived either from dissolution or from alteration of the sand after it was buried. If this is the case, the sandstone will usually be tan or yellow in colour.

Red / Pink / Orange

Another frequently seen colourant in the cementing material is iron oxide, which provides reddish tints ranging from pink to dark red (terracotta). This may provide a permanent colour from the beginning of the life of the stone, however, iron oxide rusts when exposed to air and water over time so has the potential to stain over time.

Purple

Something else that can be found in the cementing material of sandstone is manganese and if manganese is present this would provide the sandstone with a purplish hue.

Blue / grey

Most sandstones are composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface. This makes them the best choice for building materials. When there is a significant amount of clay or silt, geologists refer to the rock as argillaceous sandstone. Argillaceous sandstones are often gray to blue. This would be evidence in the texture of the stone and would be a weaker stone likely to erode more quickly making it a poor choice as a building material.

Green

Green sand is a sand or sandstone which has a greenish color. This term is specifically applied to shallow marine sediment, that contains noticeable quantities of rounded greenish grains. These grains are called glauconites and consist of a mixture of mixed-layer clay minerals, such as smectite and glauconite mica. Greensand forms in marine environments that are depleted of dissolved oxygen but rich in organic detritus and low in sedimentary input. Deposits of copper in non-marine sandstones are numerous and widespread as well and this can provide green patches within the stone. This is not to be confused with anything green that might be growing on the stone.

Biological Colouring

If an organism grows on a stone it may look at a glance like the stone has been discoloured, but in fact the stone itself has not been discoloured as the organism is growing on top of it and provides the colour. This is not of any interest to us for the purposes of this EarthCache so if you see anything you believe isn't actually a colour of the rock, please disregard it.

Please visit St. Ninian's Cave and send me the answers to the following questions via email or messenger to log a find. The questions all relate directly to the information provided in the listing so you should be able to answer everything from GZ with no extra reading required. Please ensure you send in the answers at the time or soon after you log your find, as logs may be deleted if no attempt at the answers are made.  

Question 1 - Please estimate the size of the entrance of the cave (Height/Width).

Question 2 - Please walk to the back of the cave and measure the size here (Height/Width).

Question 3 - How do the answers above confirm this cave was formed by the sea rather than another formation process?

Question 4 - How high would you say the cave is above sea level? Do you think this was always the case? What do you think has happened to the sea levels since the cave was formed? Do you think St. Ninian have lived here without being submerged at high tide?

Question 5 - Given the caves current position in relation to the sea, do you think the cave is in any immediate danger of either growing or turning into an arch in the next 1,000 years?

Question 6 - Do you think the cave is at risk in any other way such as cliff collapse?

Question 7 - What colours can you see in the walls of the cave or around the entrance? What minerals are responsible for these colours?

Finally - Please take a photograph of yourself/personal item/GPSr with the cave in the background. Please avoid any closeups of the rock that may compromise the answers. Under revised guidelines, this is now a logging requirement.

Please note. At the time of publication if you are in an area where there is no signal and you write your answers into the message center it will not queue the message to be sent later as it does with logs - instead it will be deleted immediately by the app if it fails to send. Please be aware of this as I need to receive your answers. If you don't get a pop up saying 'message sent' then it hasn't!

Thank you for visiting the 'St Ninian's Cave' EarthCache