Geological Formation of Ireland
Ireland first came into being approximately 440million years ago with the collision of two submarine landmasses. The pressure and energy created by the collison forced Ireland to the surface for the first time in history. The fusion of the two landmasses is still detectable in a line that runs from Donegal to Wicklow in the granite formed by the collision which is found in both counties and in particular in the Donegal mountains.
Over the millenia Ireland went through a number of periods below and above water for millions of years at a time. During the times below water thick layers of coral and marine debris settled forming a calcium rich layer which eventually formed the layer of limestone that covers most of Ireland and at other times a thin layer of chalk was added. When the land was above water it was at times covered in luxurious forests and swamps which laid down a layer of coal. Much of this softer coal and other rocks such as sandstone were blasted away during periods of desertification as the land moved North due to tectonic movements of the Earth's crust.
The last of Ireland's rock layers were laid down approximately 60milion years ago when Ireland was in an area of high volcanic and tectonic activity. The evidence of this is highly visible in areas such as the Giant's Causeway in Co. Antrim and the Mourne Mountains of Co. Down.
The Effects of Glaciation
Despite the millenia of geology involved in the formation of Ireland most of the current regions owe their appearance to the last Ice Age which occurred between 20,000 and 10,000 years ago. During that time the planet went through a prolonged cold period causing the Arctic ice to extend from the North Pole and to cover Europe. Ireland was almost completely covered by an ice sheet that stretched SW from Scotland. Little of the land below would have been visible with only the very highest peaks above the level of the ice.
The movement of the expanding ice sheets, its tremendous weight while it covered the land and the movement as it retreated must have had a massive impact on the land below. Of course, this can only be surmised from the evidence visible today as it's impossible to determine exactly how the land looked prior to the last Ice Age.
In the NW the movement of the ice affected the Bluestack, Derryveagh and Sperrin Mountains but due to the hard quartzite rock that forms them they were rounded rather than destroyed. Nowhere is this more evident than Errigal which stands at the edge of the Derryveagh Mountains. The ice also left the upland areas of the whole region bare of soil leaving even the valleys agriculturally poor to this day.
As the ice retreated much of the debris held by the ice was deposited as sheets of drift material. Much of this was composed of gravel, sand and sometimes clays. The irregular pattern of deposition has resulted in varying quality of land around the country. Some of it laid down in a gently undulating form has provided good for agriculture while in other areas it has hindered drainage of surface water leading to many lakes which in some cases further developed into the blanket bogs that are so well known.
The glens and valleys of Ireland were also created during the Ice Age and come in two forms. The first is a U-shaped valley which is characterised by a broad, flat bottom and steep sides. Glengesh is one of the most striking and scenic examples of this type of valley which is created solely by the movement of the ice as it scours away the softer rock and soil leaving the harder rock behind.
The second type of valley was formed by the actions of meltwater making its way to the sea during the ice age and as the ice retreated. These valleys tend to be more V-shaped and narrow and the famous Glens of Antrim are good examples.
Claiming the Cache
To log this cache as a find you must do two things:
- Research the following terms associated with glaciation in Ireland and email me a short definition of each:
- Estimate the length of the valley by measuring the road distance from the coordinates to the viewpoint. Email me this figure.
Only after completion of both tasks and confirmation of your correct answers can you log a find.
Optional Task: Please take a photo of yourself with your GPSr at the viewpoint at the SW end of the valley with Glengesh Valley in the background. Do not display the coordinates in your photo. You can post this photo in your log when you get confirmation of your answers for 1 and 2 above.
* Remember that it is good manners to wait for confirmation of your correct answers before logging your find.
* When contacting me via my profile make sure you tick the box to send me your email so that I can confirm that your answers are correct. If you don't do this then I can't reply.
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