A MEGA earthcache EarthCache

At the parking co-ordinates, Have a look at the interpretation board full of interesting information. Then look across the road and you will see something quite extraordinary......Lion Rock.

What is remarkable about this feature is that you are getting two lots of earthcache info for the price of one.

The first thing you will notice is that this feature resembles a huge lion. When natural topographic features such as rock formations resemble a person or animal etc this is known as a Mimetolith.

The island of Cumbrae is on the Great Cumbrae fault line that runs north east to south west. The fault lines have formed the lions share (excuse the pun) of mimetoliths on the island. These rock formations which have become popular with tourists, include Crocodile Rock, Indian's Face, Lion's Rock and Queen Victoria's Face. Several have been enhanced with colourful paint.

The second thing of importance about this feature which many people may not know, is that this formation is actually a volcanic dyke.

Volcanic dikes are tabular or sheet-like bodies of magma that cut through and across the layering of adjacent rocks. They form when magma rises into an existing fracture, or creates a new crack by forcing its way through existing rock, and then solidifies. Hundreds of dikes can invade the cone and inner core of a volcano, sometimes preferentially along zones of structural weakness.

The Tertiary dykes, which radiate from the vicinity of Mull and Skye, run mostly north-west to south-east. This is one of the Tertiary dykes and it consists of Labradorite with anorthite feldspar crystals. The exposure of the dyke above the surrounding landscape is due to erosion in past times, when the sea level was 10 m higher than it is at present.

The first volcanoes to affect the geology of Cumbrae occurred in the early Carboniferous period (350-270 million years ago). They were to the southwest of Cumbrae (what today is the Isle of Arran) and the dykes they produced are mainly composed of the reddish rock trachyte, forced through in a north easterly direction. The hills in the centre of the island (Terrach and Barbay), the spectacular dykes to the north of the marine station beyond the Lion Rock and the high cliff on the west side called Creagnan Fitheach, where fulmars and ravens nest, are all made of hard igneous trachyte.

Scotland saw a quiet episode after the carboniferous (the Jurassic in particular was a period of non-volcanic calm worldwide), but relatively recently, in the Eocene, violent volcanic activity returned. The northwest-southeast dykes are made of a dolerite that contains the basic silica compound olivine. The dyke at Farland Bight is made of this olivine dolerite and the fertility of surface will doubtless be noted. An extra hard, very fine-grained type of basalt was also intruded at this time. It is not known from other regions, therefore named after this island as "cumbraite". The massive "wall" behind the wooden lab at the marine station is called the De'il's Dyke (Devil's Dyke) and it and the Lion Rock are both composed of cumbraite. Note that the Lion Rock cuts right across the island, dislocated by the Ninian Brae fault and that the continuation of the De'il's Dyke can be seen across the Clyde to the right of Hunterston power station, bisected by the relentless passage of glaciers long ago.

These dykes are among the most striking features of Great Cumbrae, some standing high above the main mass of the land, which the Lion Rock, is probably the most noticeable.