Introduction
Lancaster Cemetery opened in 1855 and is situated on a hillside site which enjoys dramatic views over the city of Lancaster and the valley of the River Lune.
The cemetery and most of the buildings within its boundary are Grade II listed, including three chapels built separately to service persons of differing religious persuasions - a Roman Catholic chapel to the north, a Noncomformist chapel to the east and an Anglican chapel to the west.
The chapels, designed by prominent local architect Edward Paley, are stone-built in Gothic Revival style and situated at the highest point on the site. The entrance porches on the east and west chapels incorporate short stone pillars of crinoidal limestone - carboniferous limestone largely composed of the fossilised remains of creatures which lived in warm, shallow seas over 300 million years ago, when Great Britain lay at the equator.
Today there are no further grave spaces available to reserve, however please be aware that this is still a working cemetery as interments continue to take place in reserved graves.
The cemetery is maintained to a high standard by Lancaster City Council who have kindly granted permission for this Earthcache.
PLEASE REMEMBER AND RESPECT the fact that this is a working cemetery and also the location of several private residential lodges. The council are happy to allow this EarthCache so long as visitors treat the site with respect and behave discretely in the event that an interment is taking place.
Logging Tasks
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Based on your on-site study of the short limestone columns in the entrance porches of the east and west chapels and using the information on the cache page please tell me:
- Have these limestone columns weathered evenly? If not - please describe any differences.
- Which part of the rock these columns are carved from has best resisted the impact of weathering - the crinoid fossils or the surrounding limestone material?
- If we accept the rate of weathering of limestone as, on average, 0.5mm per 100 years, would you say that the amount of weathering on these columns is consistent with 160+ years of exposure to the elements - and how do you arrive at your conclusion?
- Based on the degree of weathering on these columns, what is the compass direction of the prevailing weather?
- 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
The Carboniferous is a geologic period that spans 60 million years from the end of the Devonian Period 358.9 million years ago (Mya), to the beginning of the Permian Period, 298.9 Mya.
During the late Carboniferous the north of England, as we know it now, was actually positioned just south of the equator and was covered by a warm, shallow sea - a perfect environment for the sea creatures which we see today as fossils in the short limestone columns incorporated into the structure of these entrance porches.
In the 160+ years that the stone has been exposed to the elements here, the stone's structure and appearance have been impacted by the effects of weathering. By measuring the effects of that weathering we can infer the prevailing direction of the weather in that time and also which parts of the stone are more or less resistant to the weathering processes.
Limestone
Limestone is a sedimentary rock, most of which originally formed by the accumulation of sediments on the sea floor (although some formed in fresh water). These sediments, which were afterwards turned into limestone rock, are composed of over 50 percent carbonate minerals.
Lots of sea creatures build shells or skeletons of calcium carbonate (chemical formula CaCO3) which is made from ingredients they extract from the sea water they live in. These sorts of sea creatures usually live in warm, shallow seas where the water is rich in those ingredients and the creatures can easily extract them. When those creatures die their shells and skeletons settle on the sea bed. Some of this carbonate material turns into a calcium rich mud but some of the fragments remain whole. Over millions of years this mixture of calcium rich mud and solid fragments gets deeper and deeper and eventually the lower layers get squeezed under the weight of the higher layers and turn into solid limestone rock in a process called lithification.
Pure calcium carbonate is bright white in colour and quite soft. You may have come across calcium carbonate like this before - it's called chalk 
. Most limestone isn't pure calcium carbonate though - it has other stuff mixed in with it like sand and silt which results in limestone of different colours - off whites, beiges, greys, blues and some is almost black. Most limestone is much harder than chalk which is good because it wouldn't make such great building material otherwise 
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What is a fossil?
Fossils are the preserved remains of plants or animals. For such remains to be considered fossils, scientists have decided they have to be over 10,000 years old. The remains of sea creatures you can see in the limestone of short stone columns are millions of years old so they definitely qualify as fossils .
The fossils which make up the bulk of the rock the columns are carved from are crinoids
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Crinoid - also known as sea lilies because some species look more than a little like the flowers of the same name (as shown in the image to the right of a rare fossilised crinoid in which the soft parts were preserved as well as the hard parts). The ancient Greeks must have thought so anyway because crinoid is from the Greek words krinon and eidos which together translate roughly as lily form or lily shaped if you prefer.
Crinoids are very much animals though and definitely not plants. Though crinoids appeared in the Ordovician (488 mya), they survived the Permian mass extinction and diversified into hundreds of species which survive, today - one of which is shown in the image at the top of this page .
Crinoids can very basically be described as upside-down starfish with a stem. The stem of a crinoid extends down from what would be the top of a starfish, leaving the mouth of the organism opening skyward, with the feathery arms splayed out to catch any passing food particles. At the bottom of a crinoid stem there's a part called a holdfast which helps to anchor the crinoid to the sea bed.
Crinoid Stem Anatomy
The soft parts of ancient crinoids were very rarely fossilised and all that tends to remain - as with all the other fossilised sea creatures we've looked at so far - is the hard carbonate parts, so most crinoid fossils are just parts of the stem.
The stem is made from disc-shaped pieces of carbonate material called ossicles which are stacked upon each other and are hollow in the middle. In the living crinoid the ossicles are held together in a long column by ligaments and skin and the column of ossicles is described as articulated (see A in the above diagram).
After death the ligaments and skin decay and the ossicles start to break apart from each other (see B and C in the above diagram). If the ossicles are quickly covered up by mud or sand they stand a better change of staying together in a column like they were in life and fossilised together as the mud becomes rock. If ocean currents get to the ossicles before they are covered up by sand or mud though the ossicles tend to get separated from one another and scattered around. This is one of the reasons why crinoid fossils can appear as individual ossicles or as tube-like columns of ossicles, short ones and sometimes longer ones.
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Typical crinoid fossil appearance - so the only parts of crinoids that are fossilised most of the time are the hard parts - the ossicles of carbonate material which, in life, are stacked one on top of the other in the long stem. Because they are little tube-like structures with a hole through the middle, some people think that they look like polo mints - the ossicle in the top-left corner of the image on the right is a good example of this.
If you're lucky enough to see a cylindrical stack of articulated ossicles that haven't been cut through, the narrow grooves around the cylinder make the stack look a bit like a bolt or a screw - which is why people sometimes call these fossils screws
More often than not though, when the limestone is cut into slabs the saw blade cuts through the length of any articulated stacks of ossicles, revealing the inside parts and you get what looks a bit like a zip with two rows of jagged teeth pointing in towards each other - like the example toward the right-hand side of the image to the right.
Weathering and Erosion
Rocks are most stable under the conditions in which they were formed. The limestone in these columns for example formed on the sea bed and would be most stable had it remained there.
Exposed, as it is today, to the atmosphere, rain water and biological organisms the rock begins to break down, its component parts changing to become substances more stable in this new environment. Geologists classify these processes as weathering - probably because the weather dictates the action of the various processes to some degree.
Processes which move parts of the rock to a different location are called erosion.
These two processes work in tandem. Weathered rock is easier to erode than solid, unweathered rock.
Preferential Weathering
Pay special attention to this next bit - because it's pretty much the key to all the logging tasks .
Some rocks are more resistant to weathering - causing them to weather more slowly. Some rocks are less resistant to weathering - causing them to weather more quickly.
In nature, for example, hard sandstone layers are often found interleaved with softer layers of shale and mudstone. When a stack of such layers is exposed to the elements, the shale and mudstone layers weather much faster than the sandstone and are worn away much more quickly.
This isn't just true of layers of differing rock types though - it can also be true of rocks of a single type - like the limestone in the columns in the entrance porches of these two chapels, for example .
The image to the right shows a rock which has been preferentially weathered. Those parts of the rock which are less resistant to weathering have worn away faster than the parts which are more resistant to weathering, resulting in a surface etched with grooves which once housed solid rock.
As laypersons we might say that the softer rock wears away quicker than the harder rock but we need to remember that it's not all down to hardness - a number of other factors come into play including the number and types of minerals the rock is made up of, how dense it is, how porous it is etc. etc.
What's key though is that it's usually not difficult to see which rocks, or parts of one rock, are better at resisting the effects of weathering because those parts literally stand out from their surroundings.
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.