This EarthCache concerns the impact of the environment on the stonework in front of you.

There is limited on street parking. You DO NOT need to enter the former Chapel grounds.

You can complete the logging task from the public street

The alteration of these rock surfaces exposed to atmospheric conditions is one of the most fundamental of geomorphic processes and is generally referred to by the term ‘weathering’.

The three fundamental types of weathering are:

• Chemical Weathering – e.g dissolution by acid rain
• Physical Weathering – e.g. freeze thaw action
• Biological Weathering – e.g lichen growth

The result is changes that weaken the rock surface resulting in what is called rock deterioration, decay, crumbling, decomposition, rotting, disintegration, disaggregation or breakdown

Studies of rates, processes and modes of rock surface, and near-surface deterioration are central to rock weathering and building stone research, conservation and management.

Gravestones provide a useful means of observing and measuring the weathering of different types of rock over relatively long and easily measurable periods of time (100 to 300 years or more).

These gravestones provide information on how such materials behave under different climatic conditions and under different intensities of atmospheric pollution. Using such information may be of use in assessing the relative durability of different types of natural building materials

Some types of rock are more easily weathered by chemicals. For example, limestone and marble are mostly calcium carbonate. When acidic rainwater falls on limestone or marble, a chemical reaction happens. New, soluble, substances are formed in the reaction. These dissolve in the water, and then are washed away, weathering the rock.

This area has both heavy industry and extensive pine forests. Some of the major pollutants that effect stonework are carbon dioxide, sulphur dioxide, nitrogen oxides and particulates such as smoke. ‘acid rain’ is almost inevitable.

Carbon dioxide is probably most familiar as a ‘greenhouse gas’, contributing to global warming, but it also combines with water in the atmosphere to produce carbonic acid. This means that natural rainfall is a weak solution of carbonic acid with a pH of about 5.6 (pH 7 being neutral and pH 0 being the most acidic).

Since the mid-19th century, air pollution has been suspected of accelerating the degradation of natural and man-made materials.

Most of the stones here are sandstone, although this EarthCache focuses mainly on the marble examples.

Concern over the rapidly progressing destruction of our buildings and monuments raises the issue of how to measure the rate of surface reduction

Techniques for measuring of surface reduction include;

• Depth measurement between weathered and unweathered surfaces
• Laser scanning
• Macro stereo–photogrammetry
• And using metal plugs as a reference surface

The amount of material removed from gravestones by weathering is often measured using a reference called the Lead Lettering Index (LLI). This index assumes that the lead lettering inserted into gravestones was originally polished flush to the surface. Over time the stone has been eroded and left the lead lettering standing proud. It is assumed that the lettering has not been eroded to any significant degree itsel

“To a geologist, a gravestone can offer information other rocks can't. It is a great place for us to collect scientific data because gravestones have got dates on them, it is not that we have a morbid fascination”, said Gary Lewis, director of education and outreach for the Geological Society of America, which is in charge of the ‘Gravestone Project’.

OTHER STONEWORK

Pennant sandstones are the local rock type in most areas of South Wales Coalfield, and makes up the majority of headstones. It is made up of about 90% quartz grains and 10% feldspar grains, cemented together with a mixture of quartz, which is very resistant to chemical weathering, and iron gives its colour.

If the matrix between the grains is distributed evenly so that all the grains are bound together, then the sandstone will be very resistant to physical weathering. If the grains are large or badly cemented or there is a higher proportion of weaker feldspar, then the sandstone is of much poorer quality.

The main weaknesses in sandstone headstones are bedding planes, which will be parallel to the face of the headstone. Rain can get behind the surfaces, which will begin to spall if freeze-thaw weathering occurs. You can see this on this site.

This is easy to gauge the extent with “Rahn’s Index”.

Rahn’s Index - Visual Weathering Classification

1. Lettering sharp and distinct. No evidence of change.
2. Lettering slightly rounded showing evidence of some removal of grains. Still legible and clear though.
3. Lettering rounded. Edges clearly being removed and some original edges removed completely. Still legible and clear.
4. Lettering rounded. All or most original edges removed, but lettering still legibe, but increasingly becoming indistinct from the surface of gravestone.
5. Lettering disintegrating. Lettering still just about legible, but now almost indistinguishable from the surface of the gravestone.
6. What lettering? Lettering virtually disappeared. Need to be able to make out date to be able to date period over which lettering has disappeared.

You are asked to complete these tasks respectfully

YOUR TASK

Look for a nearby headstone with raised lettering. Only the marble stones have lead letters.

Estimate the amount of recession between the stone surface and the now “proud” lead letters.

The date on the headstone puts a time frame on the amount of recession.

Weathering may take place faster at tparticular places, depending on the amount of water available at that site.

LOGGING TASKS

YOU MUST VISIT  THE SITE

1. How far do the lead letters protrude?
2. How long has this taken?
3. Look for a stone where the lead has fallen out. How long before the carving will be completely gone here if things stay the same in this environment?
4. Where is the most wear, sides top or middle? Most headstones face EAST. What direction, would you say, is the predominant weather?
5. Look at another headstone made of brown sandstone. How old is it? Estimate the wear using Rahn’s Visual Guide

 ~ From the guidelines: You do not need to wait for permission to log. Requiring someone to wait is not supported by the EarthCache guidelines. You should send  your logging task  answers through the message center or by email , then log the EarthCache. When I review your logging task answers, I will contact you. If there is no problem, then your log simply stands.

Don’t include the answers in your log even in an encrypted form.

You should carry out these educational tasks as required by the EarthCaching organization, as a condition of logging the cache. Logs that do not adhere to these guidelines will be deleted without notification.

If near the coordinates, you wish to take a photo of yourself and/or GPS and post this in your log that's fine

BUT PLEASE DO NOT POST ANY CLOSE UP PHOTOS OF THE ACTUAL STONES

☆☆☆ FTF Honours to _jabawokee_ ☆☆☆

PS. Whilst here you may wish to visit the memorial to the great Welsh Actor Richard Burton CBE , who was born nearby. Richard Burton, CBE He was noted for his mellifluous baritone voice, Burton established himself as a formidable Shakespearean actor in the 1950s, and he gave  memorable performances in many Hollywood films. The stone is about 20m directly behind the EarthCache, and is a stage on a "Geocache Adventure"

REFERENCES

From Inkpen, R., (2001): Gravestone Weathering, Department of Geography, University of Portsmouth

http://www.envf.port.ac.uk/geo/inkpenr/graveweb/methods.htm

https://researchportal.port.ac.uk/portal/files/5314232/Using_rates_of_gravestone_decay.pdf