Geological Secrets of Rush EarthCache
Geological Secrets of Rush
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A walk along the foreshore at Rush allowed us to view a very rare and interesting sight at the cliffs. Not being geologists, but keen earthcachers, we were, nevertheless, fascinated by what we saw.
On reaching home we began some research. We learned that the Geological Society of Ireland at www.gsi.ie describes this area as “The foreshore and cliff sections along the Rush-Loughshinny-Skerries area represents one of the best continuous successions of Lower Carboniferous rocks in Ireland and Britain, illustrating many sedimentary structures, tectonic structures and fauna. Of national and potentially international importance, this site is promoted as a County Geological Site”. Further research has shown us that six geological formations make up the impressive Lower Carboniferous succession between Skerries and Rush. They are seen in chronological order from the youngest, the Holmpatrick Formation, in the north to the oldest, the Tober Colleen Formation, in the south at Rush. The latter, ie the Tober Colleen Formation, has been described as “dark grey, calcerous, commonly bioturbated mudstones and subordinate thin micritic limestones”(Geological Survey of Ireland (GSI, 2001) These mudstones are from the Lower Carboniferous – Visean period, ie they are 340 million years old. In addition to the unusual cliff formation at GZ you will also find a hole in the cliffs. http://img.geocaching.com/cache/thumb/cebb5158-b33f-427f-9bb6-48fc3c80d055.jpg In order to claim this earthcache please undertake the following activities and answer the questions which should be sent to us using the email on our profile page. 1. Estimate the height and width of the hole in the cliffs and explain how it came about. 2. Apart from getting bigger explain what will happen to this hole in several decades from now (internet research is most likely required as it’s a different geological feature to the cliffs) 3. Make a note of the angle the rock layers are to the beach here and their average width. Now please walk 90 yards North to waypoint 1 to complete the following: 4. Observe the angle the rock layers are to the beach here and note their average width. 5. Explain why there is such a big difference between (3) and (4) 6. Note the thin layers running through the mudstone layers. What mineral is this?
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