Monday 23rd September 2013
Field Trip to The Cat’s Back
22 September 2013 we enjoyed a splendid day walking up the Cat’s Back (Crib y Garth), Black Mountains, on the western edge of Brecon Beacons National Park. This spectacular ridge (arête) created in the Ice Age rises 240 metres from the parking below. Duncan Hawley’s usual ceaseless flow of information and careful tutoring revealed the evidence of the vast plains and meandering rivers of the early semi-arid Devonian period and drew us into discussion of several phenomena on which consensus has not yet been reached.
Monday 9th September 2013
Change to indoor meeting Wednesday 18th September
The talk due to be given by Professor Bill Fitches will now take place on Wednesday 20th November. Therefore the next meeting on 18th of September will be the Member’s evening. Talks will be given by Tony Thorpe and Colin Humphrey.
Sunday 1st September 2013
Indoor Meeting 21st August 2013
Talk given by member Dr Sara Metcalf on the fossil history of sharks and rays.
Sara gave an excellent talk in which she explained that there is a 400 million year fossil history of sharks. Thought to have arisen during the Devonian period there is some evidence that they could have evolved much earlier even into the Ordovician. There are about 1000 living species. She then went on to describe their morphology and how they differ from other fish. One major difference residing in the fact that they have a cartilaginous and not bony skeleton. This, of course leads to problems of fossilisation such that the main shark fossils are of teeth, dermal denticles,fin spines and calcified vertebrae. Trace fossils are rare but coprolites are frequent.
The most important genus during the Palaeozoic was that of Cladoselache, fossils of which can be found in the Cleveland Shales around Lake Erie in North America. By the start of the Carboniferous sharks had diversified and proliferated greatly and then remained relatively stable until the mass extinction at the end of the Permian. Two groups now emerged one moving into fresh water whilst the other remained marine. By the late Triassic the first modern sharks appear. These had a much more flexible jaw which increased their advantage when in competition for food.
By the Cenozoic Era all the modern sharks are present and also the biggest shark of all time Carcharodon Megalodon which is regarded as one of the largest and most powerful predators in vertebrate history.
Tuesday 20th August 2013
Next indoor meeting is 21st August when member Dr Sara Metcalf will give a talk on Fossil sharks entitled “Palaeontology with a bite: the fossil history of sharks & rays”
Tuesday 2nd July 2013
Evening field trip to Banc Dolhelfa landslide, near Llangurig
Wednesday 17 July 6.00 to 8.00pm
Leader: Colin Humphrey
Meet at 6.00 pm at the spacious roadside café car park, 3 miles south of the Llangurig roundabout on the A470 [SN 919 756] SY18 6RX. We will postpone the trip if the weather is unsafe, i.e. wet or very windy. If in doubt check on the day with Colin (01686 412397), Bill (413967) or Michele (411343).
Traditionally we do an evening field trip each year, this time to Banc Dolhelfa (small lay-by parking SN 922 748), a huge bedrock slide, one of the largest in Mid Wales, described in detail and interpreted for the first time last year. We will begin with a short drive to the opposite side of the river Wye to view and briefly discuss the whole site. Then we will drive back to a lay-by parking next to the slide and walk around it, a distance of 1 km, including a hill climb of 170 metres, to see the evidence close-up. Those who do not wish to climb to the top can easily pause and retrace their steps back to the road. The slide is fully explained, with photographs and diagrams, in Colin’s technical paper in OUGS Journal, vol 33 (2) 2012. A pre-publication version appears on our website and can be printed (6 pps). This can also be accessed directly by googling ‘banc dolhelfa’. Some copies from the journal will also be available on the evening. Following our work the site has been registered as a RIGS. Walking boots necessary; hard hat not needed; binoculars very useful.