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Local tradition maintains that this tall plain cross, thought to date from the 9th Centuary, set in a sandstone base, with slightly expanded arms was discovered on the foreshore of Donegal Bay after being exposed by a storm. It is believed that the cross belonged to a monastic settlement near the seashore, although testing was done in the area no additional archeological evidence of a monastery in this vicinity was found. This cross was erected as a market cross by Major Thomas Dickson on a small hillock in Tullaghan village in 1778. Major Dickson's reputed reason for erecting the cross was to attract attention to the market in Tullaghan which was in competition with the more popular Ballyshannon market.
Rocks can be divided into three main groups, sedimentary, igneous and metamorphic.
Sedimentary rocks are laid down as particles of material such as sand or mud and then hardened by compaction and lithification . Fossils are often preserved in these rocks.Examples of sedimentary rocks include limestone, sandstone, mudstone, greywacke, chalk, coal and claystone.
Igneous rocks crystallise from magma originating deep beneath the Earth’s surface and may be extrusive (i.e. lava flows at the Earth’s surface) or intrusive (emplaced within the Earth’s crust, below the surface). Examples of igneous rocks include basalt, granite, pumice, obsidian, tuff, diorite, gabbro and andesite.
Metamorphic rocks are sedimentary or igneous rocks that have been altered by changes in temperature and/or pressure. New minerals grow in response to these changes and their composition depends on the composition of the originalrock, and the temperatures and pressures that affect it. Examples of metamorphic rocks include anthracite, quartzite, marble, slate, granulite, gneiss and schist.
Most sandstone is composed of tiny grains of quartz and/or feldspar because these are the most common minerals in the Earth's crust.The size of the particles can be subdivided into very fine (0.0625 to 0.125mm), fine (0.125 to 0.25 mm), medium (0.25 to 0.50 mm), coarse (0.50 to 1.00 mm), and very Coarse (1.00 to 2.00 mm). Like sand, sandstone may be any color, but the most common colors are: tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.
A river carries, or transports, pieces of broken rock as it flows along. When the river reaches a lake or the sea, its load of transported rocks settles to the bottom. We say that the rocks are deposited. The deposited rocks build up in layers, called sediments. This process is called sedimentation.
The weight of the sediments on top squashes the sediments at the bottom. This is called compaction. The water is squeezed out from between the pieces of rock and crystals of different salts form.
The crystals form a sort of glue that sticks or cements the pieces of rock together. This process is called cementation.
These processes eventually make a type of rock called sedimentary rock. It may take millions of years for sedimentary rocks to form.
Mineral hardness is also important in sedimentary rocks. Harder minerals tend to be able to travel longer distances down river systems. Quartz can often undergo several cycles of erosion, transportation and lithification ( change of sediments to rock). Zircons are persistent minerals in the environment and can often tell geologists the types of rock that were the original source rock for metamorphic or sedimentary rocks.
To claim this earth cache,you must carry out these educational tasks as required by the Earthcaching organisation as a condition of logging the cache. Contact me via my profile ( please do not post in your online log) the answers to the following tasks :
1 Looking at the base, would you say the rock is coarse or fine grained ?
2 Does the rock of the base differ to that of the cross ?
3 Looking again at the base, can you see a grain or layering pattern? If so, what direction is it?
4 Describe how the rock feels smooth/rough etc) is this what you expected ?
5 Describe any weathering you see and give explanation of how this happened.
6 In which direction, N,S,E or W, is the cross leaning ?
While not compulsary, it is always nice to see a photo from your visit.
Online logs for which I have not recieved answers for will be deleted. For further information please see See www.earthcache.org
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