Geological sites (Geosites) have been selected for scientific quality, rarity, aesthetic appeal and educational value. The Geopark Earthcaches series is based around these Geosites. Their interest may also be archaeological, ecological, historical, or cultural.
Please check the tides for this cache 
Here at Llanddwyn Island an entire plate tectonic story is recorded, from the creation of the ocean floor as a mid-ocean ridge, seen as pillow lavas, through its journey across the ocean basin where it picked up sediments, to its burial and metamorphism as plates collided and the rocks sank down into a deep ocean trench.
As you approach the island you pass pillow lavas (GC2F44T) on the beach.
Follow the footpaths to the far end of the island.
It is here that there is evidence of a destructive margin, where plates collided and one was forced (or subducted) beneath the other. The rocks in the area have been subjected to deformation, chemical alteration and metamorphism and indicate that these ocean floor rocks must have descended as a jumbled mass that tumbled down a trench lying above the descending plate.
The rocks here are called "mélange"- the French for mixture. More recent Earth movements split the mélange and filled the cracks with lava (dolerite dykes).
The rock types include lavas; quartzites; shales; intrusive dolerite dykes and limestones.
In order to complete this cache, e-mail the answers to the following: (NOTE: Please DO NOT respond to the questions in your logs. )
Research:
a) What was the name of the geologist who christened the rocks "Mélange"?
b) Can you name any other types of plate margins and their characteristics?
At GZ site:
c) How many different coloured rocks can you see?
d) Take a photo of yourself and/OR your GPS with the mélange rocks in the background.
Tectonic plate theory suggests that the crust of the Earth is split up into seven large plates and a few smaller ones, all of which are able to slowly move around on the Earth's surface. They float on the semi-molten mantle rocks, and are moved around by convection currents within these very hot rocks.
There are two types of tectonic plates - Continental Plates/Crusts and Oceanic Plates/Crusts (the Oceanic being the more denser of the two).
The point where two or more plates meet is known as a plate boundary/margin, in the case at Llanddwyn Island a Destructive Margin.
A Destructive Plate Margin colliding
Further information on the geology of Anglesey can be found on the fantastic Geomôn website:
Information was sourced from literature by Dr Margaret Wood and Dr John Conway of GeoMôn Anglesey Geopark and was used with their permission.