Pebbles at Annestown

Pebbles on a Copper Coast beach

The first beach that I visited on my recent trip to Ireland was near the small village of Annestown in County Waterford. It is part of the Copper Coast Geopark, and I wish I had known at the time that the Geopark website offers informative trail guides and an audio podcast to guide visitors on a walk around this particular area, starting at that very beach.

I was immediately struck by how different the rocks in the cliff are from anything I have seen before, and the pebbles on the windy and surf-washed shore have their own unique character. A sign-board in the car-park explains that the rocks in this location are extremely old, mostly dating from the Ordovician Period, resulting from ocean-bed volcanic eruptions at a time when the land which is now Ireland was formed near the South Pole between 460 and 450 million years ago. Movements of the earth’s crustal plates over vast eons of time have caused the land to gradually migrate northwards to its current position.

In amongst the pebbles of volcanic origin and Ordovician age are others from sources further along the coast and also, no doubt, pebbles derived from the deposits of clay, boulders, and sand that were dumped over the land surface at the end of the Ice Age 12,000 years ago as the ice melted, and which can be seen today as a yellow-brownish layer on top of the cliffs.

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

Pebbles on a Copper Coast beach

COPYRIGHT JESSICA WINDER 2014

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At Dogs Bay

Dogs Bay in Connemara has a wonderful white sandy beach composed of the tiny shells of microscopic one-celled creatures that live mostly on the mud of the ocean bed. These animals are called Foraminifera. When they die, millions upon millions of their calcium skeletons, bearing many chambers and holes, and not visible to the naked eye, wash ashore to form this unusual sand. This is such a rare occurrence that Dogs Bay beach is the only one composed of foraminifera in the northern hemisphere.

The bedrock of the land around this wonderful white sandy shore is made up of volcanic rocks including granite that has many different colour forms and patterns due to the different mineral crystals that it contains – if you get up really close to see it. The granite outcrops on the shores often have a rounded surface where ice sheets or glaciers passing over them have ground them smooth. The waterside rocks form attachments for a variety of seaweeds, along with many seashore creatures, particularly gastropod molluscs like periwinkles and limpets, whose brightly-coloured empty shells accumulate at the base of boulders low down in the intertidal zone.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

On The Burren

Natural features and man-made structures amongst the karstic erosional surface of the Carboniferous Limestone landscape in The Burren in County Clare, Ireland. These photographs show the famous Neolithic portal tomb known as the Poulnabrone Dolmen and the humble, often lichen and moss-covered, stone walls. Typical limestone erosion features include the limestone pavements with their deeply weathered clints and grikes; and solution hollows or pans also called kamenitzas. Isolated large boulders, standing out incongruously on the flat bare rock platforms, are glacial erratics dumped by receding ice sheets.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

On Garrettstown Strand

Rocks on an Irish beach

Rocks on an Irish beach

Rocks on an Irish beach

Rocks on an Irish beach

Patterns in rock on an Irish beach

Again, simply a few pictures, as a “taster” of the many photographs I have been taking, to show the incredible geology I have been witnessing on my current travels in Ireland. I will write up full descriptions and identifications with more images (as best I can) when I return home. These rock patterns and structures were captured on Garrettstown Strand, also known as White Strand or Garrylucas Beach, near Old Kinsale Head in County Cork.

COPYRIGHT JESSICA WINDER 2014

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Red Point Rocks on Grand Manan

Off the coast of Canadian New Brunswick, in the Bay of Fundy, lies an island that is split geologically in two. A fault runs from north to south in Grand Manan Island and it can be clearly seen only at Red Point in the Anchorage Provincial Park. It is visible as a diagonal line in the cliff. There are distinctly different rocks on each side of the fault.

To the west of the Red Point Fault are volcanic rocks known as the Southwest Head Member of the Dark Harbour Basalt – part the Late Triassic Flood Basalt dating from about 201 million years ago. Photographs of this type of rock showing textures and fracture patterns are shown above. The Red Point Fault itself is shown below. It is visible as a diagonal line in the low cliff structure with a stream flowing out of the fault across the shore. This is “a rare exposure of a major displacement intra-basin fault” (McHone).

The geological fault between basalt on the left and meta-siltstone on the right  at Red Point on Grand Manan Island.

To the east of the fault, the rocks are metamorphic and not volcanic. They are laminated meta-siltstones of the Long Pond Bay Formation of the Cambrian-Ediacaran Formation dating from 539 million years ago. Photographs of the colours, textures, layers, and fracture patterns in these rocks are shown below.

The Mesozoic basalts of the western two-thirds of the island conceal the ancient Ediacaran (Neoproterozoic) and Cambrian (Palaeozoic) metamorphic rocks lying below them. However, in the eastern third of the island, the rocks have all moved upward along the Red Point Fault, with the more recent strata of the Mesozoic basalts gradually being removed by erosion so that the ancient metamorphic layers are now exposed at the surface. “At least 300 meters (and possibly much more) of vertical offset is required for this juxtaposition” (McHone) … of the Dark Harbour Basalt with the Long Pond Bay Formation meta-siltstones.

Click here for a geological map of Grand Manan. The map is one of many invaluable downloads about the geology of Grand Manan made available on the website earth2geologists run by J. Gregory McHone who is a professional geologist personally responsible for much of  the mapping and research on the island, and who runs the Grand Manan Museum.

McHone, J. Gregory Mesozoic Geology of Grand Manan, Graduate Liberal Studies Program, Wesleyan University, Middletown, CT.

COPYRIGHT JESSICA WINDER 2014

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Traces – Hue maps of trace fossil patterns

Just for fun, showing how nature can inspire art, the photographs of trace fossils shown in the previous post have here been colourised by the hue mapping method to produce some bright abstract images. Click a picture to enlarge it.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved