There are 3 types of rocks: igneous, sedimentary and metamorphic. In this Park, South Dublin County Council have kindly placed a number of large boulders which enable you to compare and contrast two of these three main rock types.
To register the EarthCache as found please send me answers to the following questions.
1.Can you see reflective silver coloured flakes in Boulder A?
2. Is the rock surface at Boulder A rough or smooth?
3. Is boulder B (i) lighter or (ii) darker in colour than Boulder A?
4. Is the bedrock in this area similar to Boulder A or Boulder B?
5. Optional, but it would be appreciated, if in the log you included a photograph confirming your presence in the area!
The Cache coordinates bring you to an example of Igneous rock. Call this Boulder A. Igneous rock forms when hot liquid rock, called magma, cools. When the magma cools below the Earth's surface it cools slowly forming large crystals and is known as an intrusive igneous rock. This includes Granite, which is the rock type of the boulder here. Mind you, igneous rocks may have been metamorphic or sedimentary rocks before they melted and reformed as magma.
There are many granite bodies exposed at the surface in Ireland including the Leinster and Galway Granites. They formed below the surface of the earth but were brought to the surface either through erosion of the overlying material or due to the movement of faults.
Now walk uphill to Boulder B. Here we have sedimentary rock which forms when small particles build up layer upon layer and pressure causes them to compress and cement together over time. When rocks are weathered and eroded the resulting sediment is transported by various means (e.g. river, glacier, gravity), and finally deposited into layers before it is buried and becomes a sedimentary rock. Limestone – which is what we find here – is composed of Calcium Carbonate from the remains of marine animals and sea water. You can see Calcite running in white veins through this rock. Also if you look carefully you can make out a fossilised remains of a tiny creature that lived millions of year ago. Limestone makes up a large portion of the bedrock of Ireland and certainly so in this part of South Dublin.
If you want to learn more, the Geological Survey of Ireland is a great resource for anyone interested in Irish rocks. I am grateful to the staff of Palmerstown Library who encouraged me to place an EarthCache here as a local resource.
Congratulations to Jobber85 and the MiniCachers on being First To Find. In the circumstances a First To Find coin on its way to them.