Western Isles Rocks - Lewisian Gneiss - Geology - Isle of Lewis - Isle of Harris
The Geology of the Outer Hebrides is really important - as the predominant rock type is a Lewisian Gneiss - a metamorphic rock which is astonishingly up to 3 billion years old, making it the oldest rock in Britain - two thirds the age of the Earth.
The rocks of the Isle of Lewis and The Isle of Harris - Western Isles
Lewisian Gneiss - The Oldest Rocks in Britain - and some of the Oldest in the World. The oldest rocks in Great Britain are to be found here, in the Outer Hebrides.
As well as being spectacularly pretty, these rocks are 3 billion years old, yes they are actually two thirds the age of the Earth (what a thought).
They are also some of the oldest rocks in the World. The name of the rock - Lewisian Gneiss (of which there are many types of gneisses to be seen on The Islands ) is derived from the name of the island - The Isle of Lewis.
Metamorphic - Variations in Colour
Lewisian Gneiss is metamorphic, in that volcanic heat and pressure has altered its structure somewhat.
Originally the rocks were like granite which changed as the Earth's crust became molten and they solidified, which is the reason you can see great variations in the way the layers are displayed, ranging from the white, to pale grey and even then the really dark grey.
Lewisian Gneiss - Buried Below the Surface
Coarse Bands of Minerals Through The Rock
Lewisian Gneiss was buried a long way beneath the surface for many years For hundreds of millions of years, these rocks were buried beneath the surface which meant that the intense heat and pressures helped to form the growth of the new minerals in them.
It is thought that the original rock was probably sandstones and limestone or igneous rocks like basalt and granite
The rock is mainly grey with coarse bands of white and dark minerals through it.
The pale bands contain quartz and feldspar, whilst the darker bands are dense minerals , like maybe biotite mica and hornblend.
Two Million Years Ago - The Ice Age
About two million years ago the ice age came to Lewis. Glaciers engulfed the land and the sea forming the smooth rocky landscape you can see today.
When the ice meted twelve thousand years ago, the sea level rose - flooding river valleys and lower ground and creating the lochs and drowned valleys of the isles. As the climate improved the land became alive, soil formed and plants and woodland returned. Peat developed on the poorly drained ground and extended upwards and outwards to cover large tracts of land. It buried the natural rocks and the stone monuments that had been erected by early settlers. Later peat became the chief source of fuel for the islands.
The picture above shows the strata of the rocks at Mealista Beach - Isle of Lewis. Lewisian Gneiss is so beautiful
Opposite is the red marbling of rocks at Bosta Beach.
Scotland 500 Million Years Ago part of North America
600 million years ago, Scotland was part of the continent we now call North America. Scotland was once joined to Greenland, before The Atlantic ocean was formed, For the last 60 million years Scotland, and indeed Europe as a whole, has been drifting away geographically from North America
Callanish Stones - Great Examples of the Lewisian Gneiss
The Callanish Stones Site is in the charge of Historic Scotland. Calanais is Gaelic for Callanish - originally it was actually called Callernish - or previous to this Classerniss.
The Isle of Lewis affords one of the most complete historic stone circles in Europe - and made of one of the oldest rocks in the world - types of the Lewisian Gneiss
Sandstone Conglomerate - A slightly Younger Type of rock Found on The Islands
There are other rock types which are to be found here on The Isle of Lewis and one of these is the sandstone conglomerate which is considerably younger than the Lewisian Gneiss, being 200 million years old , which is pf course still quite old. This rock is to be seen along the coast of East Lewis and parts of Point
Rocks at Port Stoth - Butt of Lewis
Stunning Rock Formations at one of the Mealista Beaches - Isle of Lewis
The Mealista Beaches is one of the best beaches on The Isle of Lewis where the rocks show the strata. A great example of Lewisian Gneiss. Te geology of the Outer Hebrides is really important.The road past Uig meanders on through the moorland with the great Atlantic Sea on your right and passes the Mealista beaches, with their beautiful rocks and rock pools,. ..