Introduction
The Church of St Wilfrid in Market Place, Standish, Wigan is a Grade I listed building, a grading reserved for buildings of such exceptional national, architectural or historical importance that it includes just 2.5% of all listed buildings. Other well known buildings in this grading include Buckingham Palace, the Houses of Parliament and Tower Bridge.
Historic England describe this church as A rare example of a late 16th century church but this isn't a completely accurate reflection of the church's history at this location or of the true ages of various parts of the structure.
Although the central body of the present structure dates back to the rebuilding of 1582-1589, the first mention of a church on this site dates all the way back to 1205. The 14th century tower was rebuilt in 1867 in somewhat similar style, with a new spire.
The red sandstone Peace Gate forming the southwest entrance to the churchyard is a Grade II listed gatehouse, built in 1926 to remember the dead of the first world war, and later, of the second world war. Also remembered are those who lost their lives in the coal mines which quite literally fuelled industry in this region.
This church is rich in history, having seen numerous episodes of extension, demolition, re-building and enhancement dating back hundreds of years.
This EarthCache focuses on the types of stone both within the grounds of the church (and one large boulder in particular) and also those used in its construction.
The Rector of the Parish has kindly given permission for this EarthCache. Please respect the church, its staff and patrons and its primary purpose.
Logging Tasks
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You'll need to visit the two locations detailed - the published coordinates and the Peace Gate (see waypoint below). Based on your observations at these locations and the information on this page you should be able to tell me:
- Describe the stone used to build the Peace Gate - in some detail - colour, grain size, texture etc.
- At the published coordinates, describe the building stones used in the church walls here - in some detail - colour(s), grain sizes, textures etc. What type(s) of rocks(s) do you think they are?
- Describe the large boulder sitting on the ground here - in some detail.
- What type of rock do you think this boulder is? Where did it come from? How did it get here?
- 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
At the published coordinates you will find yourself up close to the church building and you'll notice that there's a large boulder here and also a rough stone trough which has undergone some repairs at some time in the past. The stone trough was once used as a sarcophagus - a stone coffin - but these days it's used to plant flowers.
What's especially good about this little corner is that it provides a spot where you can examine some different types of rock in some detail - some used as building stone, others not.
Your main objective here is to study and describe the large boulder and the stone used to build the church, and then to explain what the boulder is, where it came from and how it got here.
That might sound like a tall order but stick with it - there's plenty of information on this page to steer you in the right direction ๐.
Geology is an interpretive science. As geologists, amateur or otherwise, we need to thoroughly examine the geology around us and make observations and measurements with enough accuracy that, with the application of existing knowledge, we can interpret the geology and describe how things came to be the way they are today as accurately as possible.
Erratics and How To Identify Them
The image to the right shows a gritstone erratic resting on a bed of limestone.
An erratic, sometimes referred to as a glacial erratic, is a rock of unspecified shape and size, transported a significant distance from its origin by a glacier or iceberg and deposited by melting of the ice.
Erratics range from pebble-size to larger than a house and usually are of a different composition than the bedrock or sediment on which they are deposited.
This somewhat loose definition means that identifying a lump of rock as a glacial erratic isn't quite straight forward. We have to look at various pieces of evidence together in order to identify said lump of rock as a glacial erratic - or not, as the case may be.
As a rule of thumb, glacial erratics tend to become more rounded during the process of being transported in the ice, with polished surfaces which are smooth to the touch. As the ice moves slowly over the land, rocks trapped in it are rubbed against the bedrock, or against other rocks in the ice, grinding the rock surfaces and gradually rounding sharp edges and polishing surfaces smooth in a process called abrasion. This is similar (although on a much larger scale over much longer periods of time) to sandpaper being used to smooth wood.
These abrasive processes don't always smooth rock though - sometimes as the rocks trapped in the ice grind against each other, or against the bedrock, they leave scratches or grooves on each other's surfaces. These scratches are called glacial striations and a group of them together, all parallel to each other, is another clue that a rock was transported by glacial ice.
Glacial striations can be deep but when they are very fine and shallow, especially if the rock was subjected to further glacial polishing after the striations were made, they become less visible until light hits the rock at just the right angle.
The image to the right shows an erratic made from igneous rock - possibly a granite - covered in parallel striations which are almost vertical. Ignore the diagonal pink bands in the rock - they aren't striations.
For a larger view of this boulder click on the image.
Geology of the Wigan Area
By definition, erratics are usually of a different composition than the bedrock or sediment on which they are deposited.
By that we mean that the rock an erratic is shaped from doesn't match the rock it ends up being deposited onto, that is, the naturally underlying bedrock in the place the erratic ends up at.
This means that in trying to work out if a lump of rock is an erratic we really need to compare it to the underlying bedrock. The main problem with that is that we can't see the underlying bedrock at this EarthCache location - because it's buried under clay and soil and pavements and roads and such.
Fortunately though, the church and the Peace Gate are built from local bedrocks - sandstones of various types and colours - and so we have something to compare with ๐.
The rocks under most of Wigan, including Standish and therefore including the EarthCache location are sedimentary rocks from the Pennine Middle Coal Measures Formation, mudstones, siltstones, sandstones and coal, which are around 312 to 304 million years old.
The map extract below shows the arrangement of some of these rock types with different colours indicating different types of sedimentary rocks. I've enhanced the icon which represents St Wilfrid's to make it easier to see by turning it yellow ๐.
There are also deposits in some parts of this area of Permian red sandstones which are bit younger at around 299 to 272 million years old.
Superficial Deposits
On top of the solid bedrock layer there's a layer of more flexible unconsolidated sediments made up of substances such as clays, sands, gravels and peat. Geologists call this layer superficial deposits.
These superficial deposits are more easily moved around and then deposited by natural forces such as gravity and flowing water/ice, which means that geologists can use the arrangement of these deposits to work out where and how glacial ice has flowed over the landscape.
In fact glacial erratics, because they get moved around by glacial ice, are themselves classed as superficial deposits.
The above map extract, focused on the Standish area, clearly shows that a lot of the Standish bedrock is covered by superficial deposits associated with glacial ice - sands, gravels and till (previously called boulder clay) in this case. Thus we know that glacial ice transported sediments from elsewhere and deposited them here at some time in the past.
The map also shows a little bit of alluvium, which is clay, silt and sand which has been left behind by a river or stream.
Geologists believe the area has been glaciated at least three times, although there is uncertainty as to the number and extent of events because the ice has rearranged the superficial deposits each time, obliterating most of the evidence of earlier episodes.
The last glacial period in the UK, which ended around 12,000 years ago, had the greatest impact in shaping the landscape here.
The land was exposed to severe frost attack due to the intense cold which preceded the ice sheet as it emerged from the Lake District and Southern Scotland.
Glacial Ice Pathways
The map below shows the pathways that geologists believe glacial ice has taken in the past - flowing generally southward from Southern Scotland and the Lake District.
Also shown are locations which are known to have been the source of glacial erratics in the past.
In fact erratics are one of the pointers that geologists use to infer the routes taken by glacial ice flows ๐.
Coarse Sandstones / Gritstones
Below are some detailed images showing close-ups of various sandstones, to help you to identify any which are present at the EarthCache location:
Key to above image: 1. 'Black' gritstone | 2. Coarse-grained yellow sandstone | 3. Coarse-grained pale red sandstone | 4. Fine-grained sandstone
Granites
Below are some detailed images showing close-ups of various granites, to help you to identify any which are present at the EarthCache location:
Key to above image: 1. Eskdale granite | 2. Criffel granite | 3. Loch Doon granite | 4. Dark Shap granite
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 
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Please submit your logging task responses before posting your log.