Formation of the Wicklow Mountains
Sedementary Stage
Around 500 million years ago, the seabed of the Iapetus Ocean, the predecessor of the Atlantic Ocean, built up huge volumes of silt, mud and calciferous deposit from existing sea life, in addition to vast quantities of materials deposited through volcanic action. As these deposits stratified, the lower levels were subjected to enormous pressures and the result was mudstone and sandstone. Sedimentary rocks are typically soft and prone to erosion.These sedimentary rocks were some of the foundations from which Ireland would grow.
Metamorphic Stage
Around 420 million years ago, the tectonic plates of Europe and North America collided beneath the Iapetus Ocean with tremendous force and the bedrock was buckled and forced upwards forming the land we now know as the Wicklow Mountains. The tremendous geological forces of pressure and heat exerted upon the sandstone and mudstone changed, or metamorphosised, the sedimentary rock in to new rock types – schist, slate, and quartzite. These are metamorphic rock types and are typically more resistant to erosion than sedementary rock types. Schist is commonly found around Glendalough.
Igneous Stage
A batholith (from Greek bathos, depth + lithos, rock) is a large emplacement of intrusive, or plutonic, igneous rock (meaning that its materials do not reach the surface at the time of formation) that is solidified from cooling magma rising from deep in the Earth's crust. A batholith is formed when many plutons converge to form a huge expanse of granitic rock – the Leinster batholith extends from Dún Laoghaire in Co. Dublin to New Ross in Co. Wexford and is the largest in Ireland and Britain. Other Irish batholiths from the Caledonian period include those located in Donegal, Sligo, Mayo, Galway and south Armagh and Down. (The Mournes, while created through a similar process, only date from 60-70 million years ago).
The Leinster batholith was additionally subjected to uplift. The molten layer of the earth’s crust, magma, was also forced upwards at the time of the collision of the two tectonic plates and pooled underneath the overlying metamorphic crust, much as fluid pools underneath a blister. The rock formed by this pooling cooled slowly underneath the surface, forming plutonic granite, an igneous rock type. Igneous rocks are typically very hard and often more resistant to erosion and weathering than metamorphic rocks. In Wicklow, the cooling process was slow due to the covering of metamorphic rock above and this allowed the formation of large flaky silica mica crystals typical of Wicklow granite.
Mineral Deposits
At the interfaces of where schist and granites were formed, the mineral composition of the molten rock would have been complex and varied – and it is common in such areas for metals to be deposited. Glendalough, for example, has legion lead and a few zinc mines, while other parts of Wicklow are noted for rarer silver or copper deposits. At a micro level, the molten buffer between metamorphic and igneous rock types formed seams between the two rock types and veins of, often metal-rich, crystalline silica quartz hardened. In Wicklow, quartz veins around granite and schist tend to be white, but with a metal content they can be most any colour - common in Wicklow are shades of red, brown and even green marbling. These crystalline rock forms are typically prone to weathering and erosion.
The Role of Weathering & Erosion
Subsequent millennia of weathering and glacial erosion upon the metamorphic slates, schist and quartzite have served to expose the deeply underlying pluntonic granite domes. Continued weathering has given Wicklow’s mountains their recognisable rounded forms, making them easily accessible for walkers and geocachers alike. However, not all of the metamorphic rocks have been disintegrated and in many regions of Wicklow it is possible to see a selection of rock types on the surface that illuminate the geological processes that formed the mountains on which they lie. The geological divide between granite and schist is clearly visible in places like Glendalough where coarse silver/black granites suddenly gives way to layers of smoother, shiny grey/rust coloured schist.
Logging Requirements
To log this cache, please email the answers to the following questions via my geocaching profile:
1) At the listed coordinates, count the large free-standing boulder(s).
2) One of these boulder(s) has a distinctive relief pattern on it – speculate on how this has happened.
3) Three distinct rock types are very obvious in the immediate area; please name each type and indicate if they are sedimentary, metamorphic or igneous.
4) If crystalline quartz is present on the trail, please describe its particular colour and the form of the fragments, and speculate as to why their size and form is so. (You may wish to move south along the trail for more obvious evidence).
Please send your answers before proceeding to log a find on this Earthcache; in the event of difficulty with the answers provided I will contact you.
The Terrain
This cache can only be attempted by climbing Derrybawn mountain - the fastest route is from the trailhead waypoint provided up to the summit; it is then a short distance along the ridge. It involves a steep climb - scrambling at some points - and is accordingly rated at Terrain 4.5; for the most part, however, the ascent is terrain 3.5-4.0. It is
not suitable for younger children. The terrain is not to be underestimated and all due preparations should be undertaken and all necessary equipment and clothing worn. Due to the nature of the logging requirements, snow cover may preclude location of some of the geological features; anyhow, this cache is best done in clear weather given the views! A helpful PDF map is available on the
Wicklow Mountains National Park website. Try to pick a nice sunny day... and don’t forget your camera!!!
View of the Glendalough Upper Lake from above the trailhead
Parking & Public Transport
There is a free carpark at the Glendalough Visitors' Centre but this requires a beautiful 3km walk along the Lower Lake to the trailhead. The carpark of preference is at the Upper Lake, but currently has a fixed cost of €5 per day, payable upon admission. Please note the winter closing time was 4pm at the time of publication. Please be aware that cars parked in areas close to walking trails are inherently vulnerable and they can be vandalised or stolen. Be sure to leave valuables at home, leave your glove-box open etc.
Nearby caches
This cache will walk you along the complete route required for the very easy
Derrybawn Rolls multi (1/4.5)
GC4V2G9 and completing this might actually assist you with completion of the earthcache. The earthcache is placed very close to
Merry Christmas, Mr. Jones (4/4)
GCHCQT which has an Jasmer date of Dec. 2003; walking south towards Cullentragh, following a counter-clockwise circuit, it is possible to climb Mullacor (but unfortunately, the starting stages of the AWITG #6 Mullacor multi-stage mystery cache are out of reach on this circuit) and onwards to
AWITG #43 Lugduff 637 (1.5/3.5)
GC2DMVB. Then you need to decide on either continuing west along the ridge for the long route home (about 19km total), taking in the remaining 2 Duffs and descending following the Miners' road back around the Upper Lake (four more caches on this long route, including the
Glendalough Earthcache), or taking the shorter, but highly scenic, route of just 13km total, back via
Spink (4/4)
GCGQTV to the trailhead.
Of course, you can just go up and down Derrybawn, but where's the fun in that?
The Upper Lake car park also is the starting point for
AWITG #9 - St. Kevin's Bed (3/3)
GC1R2DG and, if there is sufficient light, is a nice way to finish your day.
The view from near the Earthcache location
Leave No Trace
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The cache has been placed in accordance with the "Leave No Trace" principles. Please respect these principles when searching for the cache. The earthcache location is in the Wicklow Mountains National Park, near the summit of Derrybawn, but access is gained by walking through woodland trails under management by Coilte.
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