This EarthCache takes you to Sowerby village in Calderdale, where it is possible to see, and feel part of the South West of Scotland - Galloway. At the side of the road, just across from the church is a memorial water fountain, to a member of a mill owning family from the Sowerby Bridge area. It is constructed from local sandstone, and a granitic rock from Galloway. This type of granitic rock is known as Granodiorite.
There are different types of rocks, which can be classed into sedimentary, igneous and metamorphic. Sandstone is a sedimentary rock, whilst Granodiorite is an igneous rock.
Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle in place. The particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, the sediment was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers. Sedimentation may also occur as minerals precipitate from water solution or shells of aquatic creatures settle out of suspension.
Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallisation either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. Granite can be white, pink, or gray in colour, depending on their mineralogy. Granitic rocks mainly consist of feldspar, quartz, mica and amphibole minerals, which form an interlocking matrix of crystals.
Now, the hills of Galloway are rough, rugid, and some are hard to get to, without sweat, effort and a fair bit of leg work on the hill, so this is a chance to see and touch part of that area. This means that it does not matter whether you are in a mobility scooter on piped oxygen, pushing a pram, from the flatlands of Lincolnshire or the Yorkshire flatlands, you can still encounter some geology here.
The Granodiorite, was formed approximately 393 to 424 million years ago in the Devonian and Silurian Periods. It is an intrusive rock.Intrusive rock forms within the crust from the crystallization of magma. As the magma pushes up from deep, it eventually slowly cools into a solid, and forms rock. An intrusive rock is any form of igneous rock that forms within the crust of the planet. Large areas of magma that solidify underground before they reach the surface are known as plutons. In the south of Scotland there are two large plutons, the Loch Doon pluton, which extends from Loch Dee north to Loch Doon, and part of which is pictured above , and the Dalbeattie / Criffel pluton, which is to the south west of Dumfries.
Map showing the locations of Plutons in South West Scotland.
The Granodiorite that we see here was formed as part of the Dalbeattie / Criffel pluton. This pluton was oval shaped - imagine a creme egg here, and had different layers of granitic rocks. The grandiorite forms the outside layer of the egg, whilst the centre contains granite, though unlike a creme egg with a defined boundary between the chocolate and cream on the inside , the granitic rock gradually changed from the edge of the granite to the granodiorite. Compared with granite, it contains a higher percentage of dark iron and magnesium, which tends to give it a darker colour than granite. It also tends to have more plagioclase (white coloured) feldspar, than orthoclase (pink) feldspar. However, when talking about colour, it can get confusing as it is possible to get pink granodiorite, and white grandiorite, both due to concentration of specific type feldspars.
This being an EarthCache, in order to log it, I ask that you answer some questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile.
1. Please refer to the above picture.
(a) Please compare the granodiorite in the blue zone, and that in the pink zone, in terms of the crystals, their shape, colour and size.
(b) What park of the memorial fountain has white granodiorite? What has caused this colour?
(c) On the rim of the bowl, there is some orthoclase feldspar, please describe the crystals, their shape and colour.