Welcome to the Church of St Michael and All Angels !
This EarthCache invites geocachers to look more closely at the rock used to build Sopley Church. The learning point of this EarthCache is to get the geocacher to become familiar with the local ‘Burley stone’ and the grading of clasts.
Everything you need to answer the questions is available by attending the co-ordinates and reading this lesson. There's no need to research anything extra online, although you’re welcome to do so if you want to.
Minerals make up rocks. Rocks are formed in many different types of environment. These can be on, or within the Earth's crust.
Sedimentary rocks are formed on the Earth’s surface from the products of weathering which then becomes cemented or deposited.
At the published co-ordinates, you will be standing in front of the church at Sopley. Much of it has been built from the local Burley Stone. The church is one of the best places to view Burley Stone in the New Forest. Once you're inside the National Park, it's unusual to see locally sourced hard building stone because it doesnt generally appear at the surface.
There are remains of old quarries for the Burley Stone in the area of Burley village, but there is very little to be seen as natural exposures today. Burley Stone is present elsewhere in the area, especially in Burley village and Lyndhurst, but has often been used to build church foundations, or is found on private property or is now covered by plaster or whitewash.
There is not much hard rock exposure in the New Forest beause the National Park mostly sits on Eocene sands and clays that were deposited around 40 million years ago. This coincided with a a long geological phase called the Eocene Optimum, when Earth’s temperature was abnormally high and the area that is now the New Forest was underneath a shallow sea located close to the Equator. The New Forest was so hot that crocodiles roamed around it (and their fossils have been found at Hordle Cliff.)
Burley Stone is a clastic sedimentary rock, and is a type of sandstone that is rich in iron. Sandstones are clastic sedimentary rocks composed mainly of sand-sized mineral or rock grains. This means the has been formed from the accumulation of pre-existing rocks. A very simplified way of thinking of sandstone is being sand that has turned into rock. It forms when grains of sand from existing rock or crystals become cemented together over time.
The formation of sandstone happens over two stages. First, sand (often suspended in water) settles and accumulates. Second, this deposited/accumulated sand is compacted by the weight of further deposits.
Clastic sedimentary rocks are often formed by mechanical weathering, the process through which large rocks are broken into increasingly smaller pieces. Also known as physical weathering, the process normally happens near the Earth’s surface. Mechanical weathering doesn't change the chemical nature of the rocks. Breccia clasts, with their more angular sides, will probably have been transported a shorter distance than conglomerate clasts, which might be more rounded because of the erosion caused during their longer, further transportation.
If you look closely at the Burley Stone, you will see large visible clasts within it. These clasts are sediments that originate from older rocks from outside the area of the New Forest. Millions of years after these Eocene sands and clays were lain, by the time of the Pleistocene epoch, (about 2,580,000 to 11,700 years ago) the New Forest had moved north from the Equator to where it is located on Earth today. It was no longer under a shallow sea, and the climate was completely different. The region was a periglacial environment, meaning it was cold, and subject to intense cycles of freezing and thawing of superficial sediments. In the Burley stone, the pebble clasts you see are Tertiary debris from the chalk-with-flint uplands of the Salisbury Plain area. These were probably transported fairly rapidly from Salisbury Plain to the Burley area during times of melting snow.
The cementation (and brownish staining) in Burley Stone originates from it’s origin near iron-rich (chalybeate) springs. There are several of these in the Burley area.
So, the Burley stone has quite a complicated past. The sand and clasts were cemented together by minerals such as calcite, clays and silica. In different types of sandstone, sometimes the grains are not visible to the naked eye and are called argillaceous sediments. The types of sandstone whose grains are visible are called breccias and conglomerates, and are termed rudaceous sediments. The degree to which the grains are rounded is a sign of how far they were transported, though this may not be apparent without a microscope. Clast (pebble) size can be grouped as fine (0.06-0.2mm), medium (0.2-0.6mm) and coarse (0.6-2mm.)
The variety of clasts within a sandstone is also a distinguishing feature of the rock. If the rock comprises of a mixture of clast sizes, and a lot of matrix, it is termed poorly sorted, whilst one that comprises mostly of clasts of the same size is well sorted. Many of the sand grains won't be visible to the naked eye, but if there is a wide discrepancy of grain sizes, this should be clearer.
To log this cache, please visit the published co-ordinates and answer the questions below. Once you have obtained the answers, please send them to me via email or through the Message Centre. You are free to log your find once you have contacted me. You don't have to wait for a reply. If there are any questions about your answers, I’ll contact you.
Logs without answers will be deleted. Please don’t include close up pictures in your logs that may answer the questions.
For the purposes of this EarthCache, please start by looking at the part of the wall under the large window on the north side of the church, closest to the path. (This is the largest window in the picture at the top of this lesson.) Just under the left side of the window is the largest piece of rock.
- Look at this piece of Burley stone. Please describe the rock (size, colour, texture, size of grains, any pebble clasts, and anything else that strikes you about the rock.)
- Thinking about the size of grains, would you say this rock is made from argillaceous or rudaceous sediments?
- Thinking about the pebble clasts in the rock, is there are a variety of visible sizes, or are they all mostly the same? Are they mostly rounded or angular? Is the rock well or poorly sorted?
- Thinking about the colour of the rock, what does this suggest about the minerals in it?
Now, I’d like you to look at a second rock under the same window. It's the one in the photo below that has been covered by the EarthCache logo. It's a little smaller than the first piece you looked at, and is visibly very different.
5. Please describe this rock as before, (size, colour, texture, size of grains, any pebble clasts, and anything else that strikes you about the rock.)
6. How does this rock differ from the first one you looked at?
7. Would you say the size of the clasts (pebbles) are fine (0.06-0.2mm), medium (0.2-0.6mm) or coarse (0.6-2mm)?
8. Optional, take a photo of yourself and/or your GPS in the general area of this EarthCache.
Good luck, and many thanks for visiting this EarthCache.
While you're down here, enjoy the church, and don't forget the original Church Micro cache (a multi) hidden nearby. You'll find the link to it here.
