URBAN EARTH - This Way Up EarthCache

Introduction

Rocks are most stable in the conditions in which they were formed. When rocks are moved to a new location where conditions differ, weathering will break down the rocks into substances which are stable in those new conditions.

When we use stone for building we couldn't possibly replicate and maintain the conditions the rocks were formed in but there are some things we can do to reduce the impact of weathering and one simple thing we can do is place the stone in a way which best protects it from the effects of weathering.

This EarthCache takes you to a Grade II listed building in central Blackburn, built in coursed sandstone rubble with freestone dressings.

Seeing the stone used in this building described as rubble you'd be forgiven for expecting something looking quite uneven and perhaps more akin to an ancient castle in appearance than what you'll actually be met with - and I wouldn't want you to think you were looking at the wrong building. The building term ashlar is usually reserved for building stones which have been shaped almost to perfect cuboids with true right angles and perfectly smooth, flat faces. The stone used in this building doesn't quite match those parameters - but it's not far off.

Logging Tasks

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Based on your on-site study of the building and using the information on the cache page please tell me:

1. Are the stones used to construct the walls of this building correctly bedded i.e. laid so that their bedding planes are approximately horizontal, just as they would have been when the sediments which formed the rocks were laid down?
   
   
2. What leads you to your conclusion?
   
   
3. Look up at the five sculpted panels with lots of people on them and you should also notice that they feature a number of animals - please name at least two of them and describe any signs of weathering on them.
   
   
4. Many of the men carved into the sculpted panels sport very substantial beards. The weathering of one man's face and beard is so pronounced that it looks almost as if he's wearing an elongated gas mask! If the panels are numbered 1 to 5 from left to right, which panel features this gas mask man?
   
   
5. Optional task: feel free to add any photographs of your visit that do not show the specific features from the logging tasks - no spoilers please. In the interests of allowing everyone to experience the EarthCache fully for themselves obvious spoiler photographs will be deleted.
   
   

Background

Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earth's surface and within bodies of water.

In simple terms then, fragments of older rocks (sediments) are transported, usually by wind, water or ice until they come to rest and then accumulate in layers which build up over time, layer upon layer upon layer. The layers are permeated by mineral-rich fluids and then, as the layers build up, the weight of the upper layers compresses the lower layers, squeezing out the water but leaving the minerals behind and these minerals, iron oxide for example, cement the sediments together to form solid rock. This process is called lithification

As the layers of sediments are being laid down over time, variations in the type, size and colour of the sediments can produce rock in which those layers are clearly visible with the naked eye. Variations in sediment size result in weaknesses in the rock called bedding planes.

Haslingden Flag

The coursed sandstone rubble which is used in the walls of this building is a particular type of sandstone known geologically as Haslingden Flag.

The rocks that lie underneath the valleys and hills of Rossendale were formed over 300 million years ago at a time when the whole of what is now the North of England was covered by huge river deltas and lagoons.

Geologists believe that sediments, mainly sands, silts and muds, were eroded from hills in an area that now includes Scandinavia and Greenland and were swept into vast river deltas and lagoons in a central basin in a position now occupied by the Pennines. The sediment settled to the bottom as the water slowed down in the deltas and lagoons. The nearest equivalent sediments of today are forming in huge river deltas such as the Mississippi delta.

Peculiar conditions in what was to become Rossendale gave rise to deep beds of hard sandstones, known geologically as Haslingden Flag. This stone has a hardness and silica content equivalent to granite and was the principal reason for the growth of quarrying in Rossendale.

Weathering and Erosion

Weathering is the breakdown of rocks at the Earth’s surface, by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material.

Erosion is the process by which rock particles are worn away and moved elsewhere by wind, water or ice.

Weathering and erosion are quite easy to spot on sculpted stone. Examples include discolouration (usually darkening), flaking surfaces, cracks, smoothing of sharp edges and general softening and loss of detail of the carved forms.

Incorrect Bedding

One of the best known causes of failure in sedimentary stone buildings is incorrect bedding.

Layered stone placed upright rather than flat is structurally much weaker and made more so if water manages to penetrate weaknesses in the stone, namely the bedding planes formed when the rock was laid down.

And so, in order to prolong the life of the stone by reducing the damage caused to it by weathering, the stone should be laid on its natural bed, with its layers / bedding planes approximately horizontal. A stone laid on its top or bottom bed will resist weathering for longer. Face bedded or joint bedded stone will weather and break down quicker.

If you've carefully read and digested the information from this cache page your tasks at the cache location should prove relatively straight forward, although you may wish to take a printed copy of the page with you so that you can check your answers while there .

Please submit your logging task responses before posting your log.