This is the second in a series of photographs of rocks at Clogher Bay on the Dingle Peninsula in the West Coast of Ireland, and they belong to the Dunquin Group from the Silurian Period. Clogher Bay is just south along the coast from Ferriters Cove which has featured in earlier postings.
In an earlier post about rock textures and patterns at Tenby in South Wales I said that some rock surfaces reminded me of elephant hide. So, shown above are a few photographs that I took of the elephant skin on a prepared specimen exhibited at the Natural History Museum in London to show you what I meant – while below are a couple of examples of the textured limestone from Tenby for comparison.
Many of the large boulders that have fallen from the crumbing cliffs down to the shores of Chapmans Pool in Dorset, England, show signs of being weathered by exposure to the elements. Over long periods of time, rain, sun, frost, chemical weathering from acid water and from biogenic elements, mechanical weathering by wind-blown sand, and abrasion by wave-transported gravel and pebbles, have removed the surface of the rocks and revealed an amazing array of textures and patterns.
Softer rock matrices have been eroded to reveal harder structures normally hidden from sight within the boulders. These structures include networks of crystalline veins, as well as trace or ichno-fossils (where the hollows of burrows excavated by crustaceans in the sediments of ancient shores have been preserved, as the sediments were consolidated into rock, and eventually the spaces have been in-filled with harder and more resistant materials). It is interesting to see how small periwinkles frequently taken advantage of the dips and hollows of these eroding rocks to find shelter at low tide.
Barton, C. M.; Woods, M. A.; Bristow, C. R.; Newell, A. J.; Westhead, R. K.; Evans, D. J.; Kirby, G. A.; Warrington, G. (2011) Geology of south Dorset and south-east Devon and its World Heritage Coast, Special Memoir for 1:50 000 geological sheets 328 Dorchester, 341/342 west Fleet and weymouth and 342/343 Swanage, and parts of sheets 326/340 Sidmouth, 327 Bridport, 329 Bournemouth and 339 Newton Abbot, Compiled by M. A. Woods, British Geological Survey, Keyworth, Nottingham.
Levin, H. L. (1990) Contemporary Physical Geology, Third Edition, Saunders College Publishing, Chapter 5: Weathering and Soils, pp 109 – 120 & 128, ISBN 0-03-031139-x.
Nichols, G. (2009) Sedimentology and Stratigraphy, Second Edition, Wiley-Blackwell, 6.4 Weathering Processes, pp 89 – 92, ISBN 978-1-4051-3592-4.
West, Ian M. 2013. Chapman’s Pool (Chapmans Pool), Houns-tout and Egmont Bight, Kimmeridge region, Dorset; Geology of the Wessex Coast (Jurassic Coast, World Heritage Site) of southern England. Internet site. http://www.southampton.ac.uk/~imw/Chapmans-Pool.htm. Ian M. West, Romsey, Hampshire. Version: 14th December 2013.
COPYRIGHT JESSICA WINDER 2014
All Rights Reserved
You don’t have to be that adventurous to find out about the geology in a given area. You can discover a lot by exploring the roadsides and urban environments. Very often the local rocks are used for buildings and sea defences; or quarries and cuttings can be seen from the car as you travel along the highway.
In Lunenburg, Nova Scotia, most of the buildings in the old part of town are wooden. However, the odd garden boundary wall is made of stone, using the local rock type. The photographs in this post, though taken on a very dull wet day, show a wall of rocks that are particularly colourful with rusty stainings from the iron minerals they contain; and they also display patterns of the thin layers or beds in which the fine sediments were laid down. The rocks are most likely to belong to the Halifax Formation, dating from the late Cambrian to middle Ordovician Periods, i.e. 499 – 470 million years ago. The original deposits of sedimentary rock have undergone metamorphosis and been converted into slates and metasandstones.
COPYRIGHT JESSICA WINDER 2013
All rights reserved