Albert Promenade is a road in the Skircoat area of Halifax, which was built for Henry Charles McCrea and was opened in 1861. He was prominent in promoting the plan to allow the people of Halifax to enjoy the Rocks and the views of the Calder Valley. From the published coordinates on a good day, you can enjoy some fantastic views from this location. To one side is a rocky escarpment, which is typical of the geology of the local area of Calderdale, where there are layers of sandstone, mudstone and shale which forms the classical stepped appearance of the Calder Valley. The rocks you see were laid down 358-298 million years ago during the latter age of the Carboniferous period, when the whole of the area was covered by a huge river delta system coming down from the North. During this time, mountains to the North were eroded and sediment was carried down and deposited, and eventually compacted to form the rocks you see in front of you today.
Sandstone
Sandstone is a sedimentary type of rock and can be either laid down by the action of water or the action of wind. In the case of the Calderdale area, it is by the action of water, unlike areas such as South Manchester where the sandstone has been deposited by wind action. Sandstone is formed by small grains of rock and commonly has quartz, feldspar and sand grains in it. There are different types of sandstone. What you see in front of you is Rough Rock. Rough Rock was quarried in the Calderdale area as it was a good source of building stone. Compared to other types of sandstone, such as Locharbriggs sandstone which is a fine grained sandstone, this is a coarse-grained sandstone. There is lots of evidence in front of you from where you stand of how it was deposited and other features such as weathering and fossils.
Mudstone
Mudstone is a fine-grained sedimentary rock. It is usually black or dark grey-brown and is often soft and crumbly. Mudstones form when very fine-grained clay particles are deposited in water. They tiny particles settle to the bottom of oceans, lake floors or lagoons or even in quiet stretches of rivers. As the mud is buried and compacted by overlying sediment, the water is squeezed out and it turns into mudstone.
Shale
Shale is also a type of sedimentary rock called clastic rock, which forms when "clasts" -- that is, fragments of other rocks or minerals -- are deeply buried and compacted in a depression. In the case of shale, the clasts are silt and clay particles. Over time, the buried sediment becomes cemented and forms sedimentary rock. The only difference between mudstone and shale is that mudstones break into blocky pieces whereas shales break into thin chips with roughly parallel tops and bottoms.
Quartz
Quartz is one of the most abundant minerals in the continental crust. It is a defining constituent of granite and other felsic igneous rocks, and is very common in sedimentary rocks such as sandstone and shale. While the majority of quartz crystallizes from molten magma, some quartz also chemically precipitates from hot hydrothermal veins as gangue. It is formed from silicone and oxygen, with the chemical formula SiO2.
There are different types of quartz –
Macrocrystalline - individual crystals visible to the naked eye.
Microcrystalline – crystals not visible to the naked eye.
There are also different colours of quartz -
Amethyst tends to be purple.
Citrine tends to be yellow to orange - it is rare in nature but is often created by heating Amethyst.
Milky Quartz tends to be cloudy white.
Prasiolite tends to be a leek-green colour – again it is rare in nature but is created by heating Amethyst.
Rock Crystal tends to be clear.
Rose Quartz tends to be pink to reddish pink.
Smoky Quartz tends to be brown to gray.
Fossils
Fossils are the preserved remains or traces of animals, plants, and other organisms from millions of years ago. There are different processes of fossilisation which are talked about in many other Earth Caches – though you don’t need that knowledge to answer the questions here.
Your Tasks
Please read the information below and answer the questions. These can be sent to me either by e-mail or message. Please send your answers at the same time as logging your find. Photo's are more than welcome in your log, but please do not include anything that will give away answers to any of the questions.
Make your way through the small gap in the wall and on to the stone in front of you for the first questions. From this point onwards, you are responsible for your own safety. Please go carefully, take your time and be aware of your own personal limits. As the sediment was washed down by the action of water, erosion took place of the riverbanks and on these riverbanks were trees like we have today. There is evidence of ancient trees at this location. What you see is fossilised remains of an ancient tree.
1. Tell me how long and how wide the fossil is. Describe what it feels like. Which direction does the short end point towards?
A short distance from the fossil, you will find evidence of quartz in the stone.
2. What colour is the quartz? What is the average size of the quartz pieces? Is this Macrocrystalline or Microcrystalline? Please explain why you think this.
Now make your way to the second waypoint (I would advise returning to the pavement and making your way to a sensible place where you can get over the wall and to the next waypoint) - from this point, please be aware of your surroundings as there are steep drops nearby. However, specialist equipment is not required. Access can be achieved with basic scrambling and care.
At the second waypoint, you will find evidence of cross bedding. If you look at the rock you will notice that the lines are at an angle whilst below them the lines in the rocks are flat. These are called bedding planes. Bedding planes are when different layers of sedimentation are laid down. Sometimes they are flat but at times they can be angled such as when they are laid down by water current. The reason why some of the bedding planes are flat and others are at an angle is because of different currents. For example, in a slow moving lagoon where sediment is laid down slowly, the bedding planes can be horizontal but as the current changes and the flow changes they can become angled. The angle of the bedding planes can help a geologist, or a geocacher, work out what way the current of the water came from.
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As in the picture, the arrows indicate the direction of flow. Sand grains were laid down until they built up and eventually tumbled downwards. This gives cross bedding.
3. Using the diagram above, please tell me which direction the flow was travelling in here when the bedding planes were laid down. Here we can see cross bedding. Was it laid down left to right, or right to left? Don't worry if you are directionally challenged, please just explain it the best way you are able.
4. To the left of the rock you have been looking at there is a year carved into the rock on the ground - tell me the year.
From here, carefully make your way down to the third waypoint - staying parallel to the wall above you is the easiest way I found. This will take you down to an alcove in the large rock above you. Have a look at the rock.
5. Does all the sandstone appear the same? Rub your hand over it - is some of it softer than other parts? If so, please tell me where the softer rock is located.
This alcove has been formed by weathering. Ultimately rocks don’t last forever. Eventually processes such as weathering and erosion cause rocks to dissolve and disintegrate. An example of this is that the sandstone in front of you originally came from mountains far to the north millions of years ago.
Weathering is a collection of physical and chemical processes. It can be because of physical disintegration of rock where it decomposes eventually into soil and loose fragments of rock which are known as clasts. It can also involve the chemical components dissolving such as in limestone where calcium carbonate is broken down by chemical decomposition such as you might find further to the North in the Craven Dales area. Weathering can involve a physical process such as a change in temperature such as ice causing gaps in the rocks to expand and then flaking of rock taking place. There is also chemical weathering which involves processes such as acid rain reacting with the rock. There is also biological processes taking place such as plant roots going into gaps in the rocks and also the process of lichens which can eventually lift the top layer of rock away.
Erosion can be caused by a number of factors. The factors which cause erosion can be abrasion which is where the rock surface is scraped by other rocks, or particles carried in the wind or rain. Imagine if you rubbed a piece of sandpaper over a piece of wood – that is abrasion. There is also corrosion which is where rocks are broken down by processes such as heat, cold, acid rain which can be seen in many of the buildings in the West Yorkshire area from the industrial age of the 19th and 20th centuries. There is also hydraulic erosion which is due to the action of water, examples of this can be seen in the Wharfe Valley near Grassington. Some rocks are harder or softer than others which means that they are affected by weathering and erosion in different ways, for example Granite is quite resistant to weathering and erosion whilst mudstone being a softer rock weathers and erodes much more quickly.
6. Looking at the rock - what process of erosion or weathering do you think has happened here?
7. Do you think this area will change over time, or will it remain the same. Please explain why you think this is.