All sorts of colourful & interesting rocks

This gallery displays a selection of the most colourful and interesting rocks that have been featured in posts here at Jessica’s Nature Blog over the past couple of years. While I am out walking on beaches, I am always drawn to the colours of the rocks, sometimes bright and other times more subtle, and the many different patterns and textures. Initially it is the way that the rocks look that is so appealing. So much of what I see seems like amazing natural abstract art. I try to frame the composition so that it stands alone as an attractive image in its own right. But then I get curious and lots of questions come into my mind. I always want to know what kind of rock is it? What is it called? How old is it? What is it made of? How did it get to look like that? What happened while the rock was buried? What are the elements doing to it now that it is exposed?

As an amateur with a keen interest in geology, I start by looking at maps. I try to pinpoint the exact location where I photographed the rock. Then I try to get hold of the correct geology map. Geology maps have a lot of information about the age of the rock, the type, the period in which it was laid down or developed, as well as the distribution of the different rock types in the locality. Often there are references to special papers, memoirs and so forth that discuss the geology of the area. Sometimes these publications are available on-line. I do a lot of Googling. Sometimes a visit to the library is needed. Libraries and the internet don’t always have the information I am seeking so I buy books too. Sometimes books about a specific place, and sometimes more general textbooks. I need those too because it is quite difficult to understand everything. Geology is a complex subject with a great deal of specialist terminology.

Once I am fairly certain what the rocks are, I try to write a bit about them in a straightforward way so that anyone else who is truly interested will be able to understand. It is fascinating. Slowly I learn more about the rocks and can fit the pieces together into the bigger picture. Walking along shorelines becomes a whole new experience when you are able to visualise the former environments in which the bedrock originated, or the drift geology was created, when you begin to understand what has happened to the strata over the millions of years since they came into being, and when you first begin to grasp what processes are affecting them once they are exposed to air. I love it when I can recognise strata belonging to the same geological period in different parts of the world, and see their differences and similarities, whether in situ or in buildings, walls and other structures. I begin to feel an enormous sense of wonder and awe, as well as an enormous feeling of humility, at this hugely significant part of the natural environment, a part on which everything else in nature depends or by which it is affected.

Cape Enrage Rocks 2

Cape Enrage is one of the many spectacular stop-off points as you travel along the north shore of the Bay of Fundy on the east coast of Canada. The cliffs are composed of thick and thin layers of sandstones, mudstones, and conglomerates that built up along river beds and valleys about 320 million years ago. The ancient river channels can be seen in cross-section in the exposed and weathering strata. The way that the rocks are fracturing and splitting up into their component layers makes many intriguing natural abstract patterns. Plant debris that piled up on the river banks as it was washed downstream in the Carboniferous period has been preserved as fossils.

Cape Enrage Rocks 1

Cape Enrage in New Brunswick, on the north shore of the Bay of Fundy, is a popular site for visitors because of its fantastic geology. The rocks are composed of Carboniferous Period Ward Point Member sandstones and mudstones of the Enrage Formation and the Cumberland Group. The almost vertically inclined rock layers in the cliff fracture and weather to create wonderful abstract patterns. The sediments that make up the rocks are fluvial in origin, originally deposited by rivers, and the exposed cliff-section shows many in-filled river channels. Large areas of rippled surface can be seen where channels are exposed; this together with chunks of rock with cross-bedding is interpreted as point bars in which the channels were constantly migrating laterally (as in present day braided river channels before they enter the sea). Localities with conglomerate composed of sandstone with rounded pebbles represent the the centre of river channels where the flow was fastest, or where flash floods have deposited heavier loads.

Rocks Near Cape Enrage

West of the promontory bearing the famous Cape Enrage lighthouse in New Brunswick, across a wide wetland valley blocked by a shingle bank, is another spectacular promontory with pine topped cliffs. The rocks here belong to the Mabou Group of The Enrage Formation, part of the Cumberland Group from the Late Carboniferous Period. My visit was a brief one and I wished I had known at the time that this is a site where  fossils may well be found. Unfortunately, I didn’t know what to look for and simply marvelled at the natural rock textures and fracture patterns without discovering their hidden secrets. Further east on the shore beneath Cape Enrage itself I was much luckier and found some plant fossils – but more of that later!

Porthmeor Rocks 2

These rocks are seen on the west side of The Island or St Ives Head in Cornwall, England. They form outcrops on the west side of Porthmeor Beach. I was fascinated by the sheer complexity of the colours, patterns and textures. As far as I can make out they belong to an un-named igneous intrusion (matagabbro or metamicrogabbro) composed of silica-poor magma which was later altered by low-grade metamorphism in the Devonian period between 359 and 416 million years ago.

The rock looks very different from that nearby which was featured in an earlier post. I was particularly drawn some outcrops which had an almost dark navy blue smooth surface but the majority of the rock surfaces were blue-grey and dirty yellow shades – some with smoother almost layered textures and others textured like lumpy porridge. The patterns were complex but included ancient splits and cracks that had been infilled with other materials of contrasting colours, giving paler or darker straight lines and angled cross lines – not to mention all the complicated later fracture patterns. There seemed to be large inclusions of other rock types too; this often occurs in granites. It is incredible that rocks of the same basic type can vary so much in their appearance within a few metres.

Rocks at Porth Kidney near St. Ives

Porth Kidney Sands in Cornwall is well known for its beautiful golden beach but it also has some very interesting rocks. The natural textures, colours, and patterns of cliff strata on the west side are quite different from those previous photographed in a rock outcrop at Porthmeor near St Ives. At Porth Kidney there are two types of rock, both dating from the Devonian Period about 359 to 385 million years ago, Many parts of the bedrock show layers that have been folded in complex ways by pressures and forces in ancient times and some of these strata have been metamorphosed by heat from a major igneous lava intrusion at a later date – but still retain evidence of their sedimentary origin in the layering effects.

Slates and siltstones of the Mylor Slate Formation are found in one area and are followed further west by Hornfelsed Slate and Hornfelsed Siltone (the metamorphosed version of the rocks) nearer to Carbis Bay. There are even some spectacularly bright blue-green patches between the layers which are likely to be some derivative of copper; and an iron-bearing stream that cascades down the cliff has converted the adjacent rocks to a striking orange colour that clashes with the green algae adjacent. The upper reaches of the shore are covered with irregular beach stones and also large boulders.