Glasgow Necropolis
The Glasgow Necropolis is a multi-denomination Victorian cemetery. It opened in April 1833, though a Jewish burial ground had opened the year before in the north-western quadrant of the land. There are approximately 3500 grand monuments in the Necropolis, although about 50,000 individuals have been buried here, which is usual for the Victorian era when only a small number of burial were marked with a monument.
With a growing population, and not all attending church, Glasgow was in need of an alternative to parish churches being responsible for burials. With the creation of Père Lachaise Cemetery in Paris there were calls for similar facilities in Britian, this was enabled with a change in the Law and the passing of the 1832 Cemeteries Act. Though interestingly planning of the Necropolis seems to have begun in 1831 by the Merchants' House of Glasgow in 1831, in anticipation of the new law, which allowed burial for profit.
The cemetery is laid out as an informal park and lacks the formal grid layouts of later cemeteries. This layout is probably more suited to the hill location. The statue of John Knox sitting on a column at the top of the hill, is from 1825, and predates the cemetery. The main entrance is approached over a bridge, designed by David Hamilton, that was completed in 1836 and crosses over what was then the Molendinar Burn. It became known as the "Bridge of Sighs" because it was part of funeral processions route.
Weathering
Weathering is the process that breaks rocks down. There are three main types of weathering, physical, chemical and biological. Weathering is often confused with erosion, though they may sometime happen together, they are two different processes. Weathering occurs in place with no direct movement or transport of the broken down rock. When the rock debris is moved from the where it formed then that is erosion. The same agent, such as water or ice, might cause both weathering and erosion only if the rock fragments move is it erosion, if they remain it is weathering.
Source: Geologycafe.com
Physical Weathering
The main causes of physical weathering are due to the effects of changing temperatures. Either directly causing the rock to break apart or with the assistance of water and ice.
The main types of physical weathering are:
- Freeze-thaw occurs when water continually seeps into cracks, freezes and expands then melts and then repeats the cycle, eventually breaking the rock apart.
- Exfoliation happens when there are changes in temperatures with a day - night range of 40 plus degrees centigrade such as in a desert. Because rocks are relatively bad conductors of heat, only the outside few millimetres are affected. Also known as ‘onion skin’ weathering or differential expansion as different coloured minerals expand and contract at different rates.
- Dilation is the expansion of rocks by removal of overburden such as when ice sheets melt and retreat which then develop cracks parallel to the land surface as a consequence of the reduction in confining pressure.
- Salt weathering happens in the presence of saline solutions and cause crystals to grow, particularly in shady conditions. This causes flaking of surface or small weathering pits and is faster in marine locations.
Physical weathering happens mostly in places where the rock is exposed or with little soil cover or few plants growing, so typically in mountains or deserts. The products of physical weathering are smaller fragments of the original rock.
Chemical Weathering
Chemical weathering happens when water reacts with the mineral grains and crystals in rocks to form new different minerals, mainly clays, and soluble salts. These reactions occur particularly when the water is slightly acidic. These chemical processes need water and occur more rapidly at higher temperature, so warm, damp climates are best. Chemical weathering (especially hydrolysis and oxidation) is the first stage in the production of soils. There are different types of chemical weathering, the most important are:
- Solution is the removal of rock in solution by acidic rainwater. Limestone is weathered by being dissolved by rainwater containing carbon dioxide (carbonic acid).
- Hydrolysis comprises complex chemical reaction affecting the minerals found in igneous and metamorphic rocks and is sometimes called rotting, such as china-clay (kaolinite) produced from feldspar in granite. It is also known as spheroidal weathering, as it rounds off corners of the in situ blocks of rock. As well as the producing clay minerals it produces other soluble salts.
- Oxidation is the breakdown of rock by oxygen and water, often giving iron-rich rocks a rusty-coloured weathered surface.
- Hydration affects minerals with the capacity to take up water. They increase in volume, which sets up stresses within the rock and this cause surface flaking.
Chemical weathering tends to be concentrated at rock surfaces such as fractures, joints and bedding planes. The products of chemical weathering are: secondary (mostly clay) minerals; resistant inert minerals like quartz and soluble products that are dissolved and removed by percolating water eventually reaching the sea and keeping it salty.
Chemical weathering is most intense in warmer and wet climates like the tropics, but can happen wherever there is the necessary moisture and the minerals of the rock as susceptible to the chemical processes.
Biological Weathering
Biological weathering is caused by living organisms, they contribute to the weathering process in many ways:
- Trees put down roots through joints or cracks in the rock in order to find moisture. As the tree grows, the roots gradually prize the rock apart.
- Many animals, such as piddock shells, bore into rocks for protection either by scraping away the grains or secreting acid to dissolve the rock.
- Even the tiniest bacteria, algae and lichens produce chemicals that help break down the rock on which they live, so they can get the nutrients they need.
Rate of Weathering
There are several factors that affect the rate of weathering:
- Degree of exposure to the atmosphere,
- Composition of rock,
- Climate.
The degree of exposure of rocks to the atmosphere can significantly affect the rate of weathering. Those rocks that are covered by soil and vegetation are less affected by weathering because they are less exposed to elements that cause weathering. Different rocks have different mineral composition and different minerals have different chemical composition. Some minerals are more reactive when mixed with water, oxygen or other elements and will weather more rapidly, while others will weather slowly. Also, some minerals are softer than others and they will be more affected by weathering than others. Climate affects the temperature and rainfall of a region. Both temperature and water are important elements in weathering. Warm, humid environments will have higher rates of weathering than cold, dry environments.
Geology of the Glasgow Necropolis
The low but very prominent hill to the east of Glasgow Cathedral is formed of a different rock to that which is found under the rest of Glasgow. Most of Glasgow is built on sedimentary rocks from the Upper Carboniferous Period or Coal Measures from roughly 320 to 300 million years ago. There are coal seams which were mined. The hill the Necropolis is built on is formed by a small igneous intrusion from the younger Permian Period. The Carboniferous rocks were already tens of millions of years old when this relatively small body of magma was forced into them. This igneous rock, which has fine but visible crystals and is a mixture of the minerals feldspar, pyroxene and olivine, it is called dolerite.
The Rock Exposure
There is a small wall like rock exposure just below the summit of the hill the Necropolis is built on. It is about 20m long, slightly curving and just over 2m tall at it highest. The rock can be seen between several memorial stones. The sketch below indicates two areas or sections to be studied.
Sketch of the view from the earthcache coordinates looking directly east.
Logging Tasks
To log this EarthCache answer the following questions:
Section 1 is immediately left of Jane Fulton wife of John Buchanan of Glenlora.
1 - Look at the size and shape of the blocks of dolerite in Section 1. What size are the blocks or how closely spaced are the joints that form them does this change in the section (look top to bottom)? What shape, are the blocks, how angular are the edges? Is the rock stained?
2 - What type of weathering is evident in Section 1?
Section 2 is in the corner immediately right of the mausoleum wall.
3 - Look at the size and shape of the blocks of dolerite in Section 2 (be careful to look at the rock exposure and not the cement bound boulders in the mausoleum wall). How closely spaced are the joints that form the blocks, does this change in the section? What shape, are the blocks, how angular are the edges? Is the rock stained?
4 - What type of weathering is evident in Section 2?
5 - Do you think that the construction of the Necropolis has affected the type of weathering observed in Section 1 or Section 2? Explain your answer.
Send your answers through my profile at geocaching.com either e-mail or message center. You don't have to wait for me to approve your answers. Once you send your answers feel free to log this EarthCache as found. If there are problems with your answers, I will contact you.
Sources
BGS.ac.uk
Geolsoc.org
Wikipedia.org
Geologycafe.com
