The Upper Swansea Valley played a major role in the birth of the industrial revolution. The hard anthracite coals and substantial limestone deposits found in this part of Wales were two essentials for the smelting of iron. The geological history of this lovely part of the Brecon Beacons National Park has consequently been well researched. Today its geology is still a major economic influence only now it is tourists who are supporting the local economy. They come to see the caves, waterfalls, mountains and river valleys which are the most visible results of a dynamic geological past.

It is now around 550 million years since the older rocks in the Upper Swansea Valley were formed. This was in the Cambrian Period, at the beginning of the Palaeozoic Era, when life on Earth was becoming established. The Era ended with the Permian Period which saw great upheavals in the earth's crust and mass extinctions of many life forms. Today evidence of their existence is to be found in the rocks of the area, such as at Nant Llech, which is renowned for its fossils of Westphalian fauna.

The rocks also tell the story of an incredible journey through the ages and were the subject of some of the early work which defined the chronology of the Palaeozoic Era 

 

 

 

An Incredible Journey

During the Palaeozoic Era 550-290 million years ago, the tectonic plate upon which Wales is situated moved Northwards from a position some 40 degrees South of the Equator (the present latitude of New Zealand) to 25 degrees North of the equator (the present latitude of southern Egypt and the Sahara Dessert), a distance of around 5000 miles. Since then it has continued to move a further 2000 miles Northwards to its present position of 52 degrees North. 

Life was just beginning on Earth at the time that these dynamic events began. The movements and changes that the area has witnessed since then makes the word "dynamic" seem very appropriate. From the temperate "Southern Ocean" to a cool Northern latitude, via the two tropics and the equator, is quite a journey in itself. When viewed in three dimensions however we can see that the region also spent millions of years on the ocean floor, and was  "heaved up" above sea level and re-submerged again several times, on what was a geological roller coaster ride.

Rocks and their structures help us to unfold the long story of Earth's history. Around Abercrave the rocks are are mostly sedimentary, which means that they formed from deposits of mud, silt, and sand in waters of variable depth. Most were deposited in the sea but some formed in river beds or even on land as sand dunes.

It is in such sedimentary rocks that ancient traces of life are preserved as fossils, which can tell us not only about the particular life form, but also about its environment at the time that it lived. In the case of South Wales these ancient environments were very different to the one we experience today, and by weaving together all the threads of  information we can read the story of Wales throughout the Palaeozoic Era (550-250 million years ago).

 

 

The Abercrave area has strong geological connections reaching back to geology's origins as a science. Professor Adam Sedgwick ( 1785 to 1873 ), Cambridge Professor of Geology worked extensively in the area and named the Cambrian System after the local Cambrian Mountains. His assistant who helped him to categorise the many samples was Charles Darwin, who went on to propose the theory of evolution.

Sir Roderick Impey Murcheson who defined the Palaeozoic Period also worked and studied for many years in Wales. His naming of the Silurian System came from the Silures, who were a local and warlike Celtic tribe in Roman times.

Here is how Murcheson justified his choice of name for the Silurian System......

"The Roman Historians afford no correct account of the geography of this region, but they assure us the Silures were, of all the nations in South Britain, the most powerful and warlike, impatient of slavery and of great intrepidity. Such was their confidence in their gallant leader, Caradoc who they called Caractacus, so exasperated were they at the saying of the Emperor Claudius that the very name of Silures must be extirpated, that they carried on a stubborn war...

British geologists will therefore not doubt that Silurian is a name entitled to be revived when they are reminded that these struggles of their ancestors took place upon the very hills it is proposed to illustrate under the term Silurian System."

 

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We thank Mr Mike Allen MSc  of Swansea University for his contributions and the inspiration which helped to make this site a reality.

Professor Alan Sedgewick

Located in an area of remarkable geological diversity in the Brecon Beacons Geopark,

Sir Roderick Impey Murcheson

The area is defined by large deposits of anthracite coal and limestone, the two essentials for the smelting of iron ore and subsequent steel production.

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Coal & Metals
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