The Pembrokeshire Coast National Park displays a greater variety of geological features and associated landforms than any equivalent area of the same size in the British Isles. The coastal scenery was the prime reason for the National Park's designation.
Pembrokeshire has 50 Geological Conservation Review (GCR) sites, of a total of only c.400 in the whole of Wales. These sites are, at least, of national significance and some are of international importance. T
The cache coordinates are located on a small headland in Whitesands Bay
The primary rock type on St Davids Head is gabbro; an igneous rock (meaning the rock has been formed from prehistoric lava flows) Gabbro is an intrusive and mafic igneous rock. This basically means it is high in magnesium and iron compounds. Mafic igneous formations are created in lava flows which weren't very thick (low viscosity.) The opposite side of this spectrum is felsic - where igneous rocks are full of quartz and feldspar.
The gabbro is formed in distinct layers or planes as they are known geologically.
The cache coordinates take you to a small headland known as the Ram's Nose. From here you can see the distinct layering in the cliffs and the variations of the rocks within. The coordinates are a great vantage point to observe the geology of the coastline. With your back to Whitesands Bay you should see a small stack of gabbro. This is known as a pluton ( a large mass of igneous rock). If you observe the cliffs to the right of the stack you will see there is a distinct layering of black.
This is known as rhyolite - another example of a pluton. This is an example of a volcanic intrusive feature.
In order to claim a find on this earthcache you will need to perform the following tasks.
1) Estimate the height of the gabbro pluton
2) Which intrusive feature is the Rhyolite near the gabbro pluton? You can use the diagram in the listing provided. Describe what you see and why do you think this?
3) Would rhyolite be classed as a Mafic or Felsic rock? Please explain your reasoning.
Please send the answers to the questions via my my geocaching profile. Don't wait for my confirmation before logging a find.
Pictures are appreciated.
Thanks to NT for the permission.