GEOLIDAY - SOUTH A week in the field, in South Devon 16-22 April 2005 Led by Dr Roger Beck. Reports by Patricia Taylor, Terri Hudson and Tom Miller

Blagdon Manor, Collaton St Mary, Torquay - the base for the 2005 OUGS Walton Hall Branch 'Geoliday' in South Devon. A Domesday Manor with a ‘recent’ extension built in 1537.

Blagdon Manor, Main Entrance Blagdon Manor, East Wall & Garden

Day 1 - Saturday 16th April - Cox Tor, Merrivale Down, King's Tor and Burrator Quarry

After the snow and rain that greeted us as we arrived at Blagdon Manor, our first day in the field started slightly grey but with a promise of better weather to come. We assembled into the convoy of cars that was to become our trade mark for the rest of the week, and set out for western Dartmoor and our first location of Cox Tor.

On the summit of Cox Tor, looking east We climbed the sedimentary layers with cherts to the top of the ‘Tor’. This tor, rather than the expected typically rounded granite, was a fine grained dark crystal of an early Carboniferous dolerite sill. This coarse grained mafic intrusion pre dates and has been metamorphosed by the later intrusion of the granite. By the time we reached this vantage point, the sun had come out and we had a great view of Dartmoor and out to sea giving us an idea of the scale of the granite underlying this region.

Periglacial Stone stripes on Great Staple Tor Looking east from the summit of Cox Tor, we could clearly see the granite top of Staple Tor. Roger posed the question, did the tors escape the periglacial conditions of the Devensian glaciation? The concensus was 'yes', they were some distance from the southernmost limit of the ice sheet, but one could clearly see stone stripes (cold period surface features) snaking down from the summits of Staple Tor. There was evidence of early human settlement here on the slopes of Cox Tor. Stone circles and enclosures.

Lines of Stones, Marching to the Horizon Leaving Cox Tor, we headed east to Merrivale Down. Up on Merrivale Down there was further evidence of early human settlement. Here, there is an impressive three sets of parallel lines of stones and numerous circles from pre- historic settlement.

Stones for Bridge - Rejected! Following the disused railway line, which was formerly used to transport granites from the quarries, we circled the summit of King's Tor. On the west side of King's Tor, we inspected some of the quarried and rejected stones for London Bridge, abandoned beside the track.

Burrator Quarry exposing the irregular granite- pelite contact Finally, we paid a brief visit to Burrator Quarry, where we saw a rare exposure of the contact between the Permo-Carboniferous Dartmoor Granite and the Devonian country rocks of the Kate Brook Formation. In evening sunshine we returned, tired, to Blagdon Manor. A splendid meal awaited, prepared by Linda Holmes and Mike Henty.

Day 2 - Sunday 17th April - and Thurleston

Sunday started out dull and overcast. We set off in convoy southwards towards Hope Cove. The weather worsened as we approached the south coast and was drizzling steadily by the time we assembled in the lay-by at Inner Hope.

Hope Cove, Looking North We were right on the edge of the Start Point Complex. Roger ushered us down to the narrow cove, where we spent a little time examining the deformed rocks below the sea wall. Here there were grey schists and green schists with a steeply dipping cleavage. Strike east-west. There were also blocks of red sandstone amongst the schists. The south wall of the cove was very steep. Looking closely in the south wall of the cove, one could find slickenside surfaces dipping very steeply southward. This is the western end of the Start Boundary fault.

View north-west towards Thurlestone and -on-Sea We climbed up from the cove and followed the path southwestward up onto the hill. The weather was worsening. However, looking back northward, Roger was able to point out the folds in the land across to Thurlestone and further to Bigbury-on-Sea.

Unconformable contact of Permian sandstone and breccia resting on the Devonian Meadfoot group at Thurlestone Rock We returned to the cars and drove to our next location at Thurlestone Rock, near Thurlestone. In driving rain, we could do nothing but remain in the cars in the car park. We had lunch and waited for the rain to abate. A respite in the weather allowed us to spend a little time on the cliffs at Thurlestone Rock. Here, there is a splendid contact of the Permian Exeter Group (breccias and sandstone), resting on the Lower Devonian Meadfoot Group (well-developed foliation, discoloured red

from the sandstone above.

As we returned to our vehicles, the weather turned bad again. Roger elected to finish the day at this point (due to the weather) and we we returned, rather damp, to Blagdon Manor. We were (of course) absolutely ready for the dinner to come, prepared by Linda and Mike. Day 3 - Monday 18th April - Dawlish Warren and Coryton’s Cove

The weather was changeable with lots of cloud as we headed to Dawlish Warren to join Linda Fowler, our leader for the day. Our walk along the beach and sand dunes towards the estuary mouth spit gave us a chance to look at the various types of sea defences including rock armour made from Norwegian larvikite used to dissipate the energy of the waves and gabions.

Groynes and Rock Armour (in the background) Gabions (broken rocks in steel baskets)

We looked at the beach and estuarine depositional processes occurring today in the Exe Estuary. Here we could see how sand bars form both inside the spit (flood tide delta), and outside the spit (ebb tide delta). Bedding in the modern dunes on Dawlish Warren Spit Before we left the Dawlish Warren spit, the weather started closing in and we took refuge in the Dawlish Warren Nature Reserve Visitors centre, just as the heavens opened. After lunch we took the train to Dawlish and walked along to Corytons Cove. By this time the sun was blazing down on the exposures of glorious red sandstones formed by very rapid

erosion during the post Variscan orogeny.

Roger examines the fluvial bedded sandstone at Coryton’s Cove (looking for granite pebbles from Dartmoor) From Coryton's Cove, we walked back alongside the railway to Dawlish Warren. We studied the exposures in the cliffs beside the railway. These exposures from the bottom of the Dawlish Sandstone formation showed superb examples of cross-bedded sandstones that were interleaved with breccias. These represented a repeating sequence of depositional conditions from fluvial to aeolian and back to fluvial.

Aeolian Sandstones, Beside the Railway Fluvial Sandstones, Beside the Railway

At the end of the day, on return to Dawlish Warren, we thanked Linda for an enjoyable trip and set off for Blagdon Manor. Another excellent meal awaited, prepared by Linda and Mike.

Day 4 - Tuesday 19th April - Prawle Point, Hallsands, Beesands, Torcross and Slapton Sands

Tuesday morning we set off to the south coast again, to the Start Point Group at Prawle Point. After a rainy drive, we arrived at the NT car park at Prawle Point where the weather brightened considerably. It was lovely. Roger led us down to the rocky shore where there were exposed the Devonian mica schists and chlorite/hornblende-epidote schists of the Start Point Complex. These rocks can be distinguished, in ideal light, as dark and light bands along the shore. There were also large quartz veins.

Hallsands Hotel, above the former site of Hallsands Village From Prawle Point we travelled northeastward to Hallsands, crossing the Start Boundary Fault near South Allington. On arrival at Hallsands, we parked in front of the old Hallsands Hotel (now abandoned) and pondered the coastal erosion that is occurring there. In January 1917, the village of Hallsands was taken by the sea, after offshore dredging had removed shingle for the expansion of Keyham Naval Dockyard. The beach at Hallsands is cut through by the Start Point Fault. Here, the schists show a very well developed cleavage, with an almost vertical dip and east-west strike. Roger posed the questions 'Which direction is the circular current around Start Bay?' and 'From which direction is the material transported?'. It was not clear at this stage.

Pamela Houseden beside the slate at Sunny Vale Quarry, Beesands From Hallsands we moved northward up the coast to Beesands. At Beesands, we found no schists. Instead there is a slate quarry and a dolerite intrusion. It seems, the circular current around Start Bay is anti-clockwise. Material seems to have been moved along the shore in a southerly direction.

From Beesands we moved northward again, to Torcross. As we descended the hill towards the coast, the village of Torcross came into view with the Slapton shingle bank stretching away towards Slapton Sands in the north. Torcross and the Slapton Shingle Bank separating the Ley from the sea We discussed how shingle banks like Slapton Sands are formed. No firm conclusions were reached, but the majority felt it was linked to interractions between tidal headland eddies and the anticlockwise rotating current around the bay. A walk along the shingle bank revealed pebbles of granite brought down

from the tors by the River Dart.

Sherman tank, Torcross Memorial (the tank was recovered from the sea where it foundered during the practice D-Day landings) At Torcross is a memorial to several hundred American soldiers (more than 700 men) who were killed in 1944, during training preparations for the D-Day landings. A Sherman tank, recovered from the sea bed, provides the memorial centre piece.

On the return from Slapton Sands, we stopped briefly on the Slapton road to look at an exposure of the Permian Exeter Group, breccias and sandstones.

Day 5 - Wednesday 20th April - Goodrington Cliffs, Triangle Point and Hope’s Nose

The day dawned with a promising blue sky, and after the usual excellent breakfast we made our way to the first stop, the Cliff Park Road car park. While waiting for everyone to arrive and don boots, etc, Paul initiated a game of basketball for those energetic (and brave) enough to join in. Our leader, Jenny Bennett arrived with her enthusiastic demonstrator (Prof. John Mather), and after being reunited with her OUGS friends and a member of her very first student group as an OU tutor back in 1995 (and still studying Earth sciences today), the day’s geology began.

Large Fossil Burrows First we saw rocks described to be like a fruit cake by the Torbay coast and countryside trust’s guide to Saltern Cove, which were the alluvial fans deposited at the base of desert mountains. Then we saw some quite large fossil burrows, prompting discussion about what animal could have formed them, and the happy snapping of digital cameras.

Jenny Bennett points out the contact of Limestone breccias unconformably on purple Devonian slates Turning the corner into Waterside cove, we saw the unconformity where the purple Devonian slates are overlain by the imbricated limestone breccias of the New Red Sandstone. On the south side of the cove and across a fault, Upper Devonian Rocks with vertical bedding disguised by strong horizontal cleavage, with tiny pyritized fossils awaited inspection. Between Waterside cove and Saltern Cove lies a goniatite bed, which apparently needs further investigation by someone keen enough to take it up for their MSc.

Ice Creams! Saltern cove offered further treasures, such as a fault face with a mass of calcite veins, folded red mudstones, limestones and volcanic beds. The way back took us over Sugar loaf hill, just for the exercise, and some of us enjoyed an ice cream.

Triangle Point A leisurely drive to the next location, Triangle Point was followed by a leisurely lunch and another ice cream. Then the legs began to shake, as Triangle Point is a limestone ledge tilted by faulting to a frightening degree. For those brave enough to climb it and have a look, there are stromatoporids linked and bound together by chain- like growth of tabulate corals.

Small Quarry at Daddyhole Cove Behind this was a stunning fault face with recystallised pinkish calclite. Across this we visited a quarry at Daddyhole Cove. The logistics of bringing a boat close enough to ship the building stones was discussed. It had been in this quarry that a small amount of gold had been found.

Raised Beach with many oyster shells, at Hope's Nose At Hopes Nose we visited quite a spectacular raised beach. There had been a problem with dating this beach. There were many shells, but they were too old for carbon dating. Jenny had done work on these during her MSc, and had managed to date the shells by examining how much of the chiral centres of the amino acids within them had epimerised from being naturally left handed to right handed (the amino acid racemization ratios). Clever, eh? Then it was back to Blagdon Manor to see what culinary delights awaited us that evening.

Day 6 - Thursday 21st April - Moretonhampstead, Sticklepath Fault, WBB Minerals Quarry

Thursday was the day we followed the line of the Sticklepath Fault, tracing its axis through the region from near Stcklepath, south-eastward to the Bovey Basin. After breakfast we made our way to Moretonhampstead and then onto some high ground at Shapley Corner, west of Moretonhampstead. From up here, we could see the country to the northwest, through northeast to southeast, marking the line of the fault. Roger explained that the Sticklepath Fault is not a single, well-defined feature, but a complex of faults that underlie the valley southeast through the Bovey Basin to Torbay. We returned to the cars and drove east to Blackingstone Rock. This is one of the easternmost tors of Dartmoor granite. We all climbed Blackingstone Rock to get the view of the country from its flat top. The view from Blackingstone Rock gave us another perspective on the Sticklepath Fault complex, this time from the eastern side. While on Blackingstone Rock, Roger suggested we all take a final look at the Dartmoor granite beneath our feet. Large crystals of feldspar were clearly visible.

Blackingstone Rock

The Granite of Blackingstone Rock

Trenchford Lake Continuing south now, through wooded country, we passed beside the water reservoirs of Kennick, Tottisford and Trenchford lakes. We stopped for a while on the dam at the end of Trenchford Lake. This is a very attractive and peaceful area. The water reservoirs are testimony to the underlying deposits of kaolin (china clay) that weathered from the granite bodies nearby, and their linear arrangement shows clearly the erosion along the lines of weakness of the Sticklepath fault zone.

WBB Preston Manor Works, Southacre Quarry Our next objective was lunch. Roger had earmarked a very pleasant location for this, at the village of Lustleigh, but sadly there was insufficient parking space there. We proceeded directly to the WBB Preston Manor Works, Ball Clay Quarry near Knighton. We had lunch in their visitor's car park (Not as picturesque as the village of Lustleigh, but perfectly adequate). We were joined shortly by Martin Milne, Devon Forecasting and Planning Manager of WBB Devon Clays Ltd who led us out to the clay pit workings. While overviewing the main quarry, he outlined the geology of the Bovey Basin and gave a detailed commercial history of the WBB business.

Ball clay grinding plant, WBB Preston Manor Works Subsidence along the Sticklepath Fault in Tertiary times accumulated a great thickness of kaolin clay, sand and mud with large amounts of plant debris. A lake formed at least 10 miles long, fed by streams coming off Dartmoor. Plant fossils dated the sediment as Oligocene (about 30 ma ago). The clays at Bovey are worked through opencast extraction for the production of high grade earthenware, drainpipes, tiles and bricks. The fossil plant debris (lignite) in the ball clay gives fuel for firing in the potteries.

After a excellent tour of the Southacre Quarry and Ball Clay Works, it was back to Blagdon Manor for dinner, care of Mike and Linda.

Day 7 - Friday 22nd April - Budleigh Salterton Pebble Beds

Sadly, this was our final day in the South Devon region. On our way home, we were to visit Budleigh Salterton near Exmouth for a look at an enigmatic, Triassic deposit that outcrops in the coastal cliffs just west of Budleigh Salterton. We took our separate ways to get there and arrived at the Otter Estuary car park, in dribs and drabs, as the weather turned to rain. Roger walked us along the pebble beach toward the cliffs and pointed out the differing beds in the cliff face, dipping gently to the east. Roger asked us for our explanations...... Budleigh Salterton Coastal Cliffs At beach level, we could see a gravely/pebbly conglomerate, overlain by a distinct, yellow sandy horizon. This, in turn, is overlain by a great thickness of poorly cemented sand, which showed much honeycombe weathering. Here and there, the suggestion of aeolian dune cross-bedding could be seen in the upper sandstone.

Cliff Section Group Study The group closely inspected all of the bedding that could be reached. At beach level, the pebbles and gravel were matrix supported and interbedded with fine sand. This graded upwards to smaller pebbles and gravel only (grain supported), without sand, beneath the yellow sand horizon. A desert environment? Someone found aeolian abraded pebbles (dreikanter) just beneath the yellow sand horizon. So, we had a conglomerate, with a wind abraided top surface. Nobody could offer any suggestions as to the nature and origin of the yellow horizon immediately above the conglomerate. Roger ultimately put us out of our misery by pointing out things we had not noticed; i.e. The presence of braided river bedforms in the conglomerate (not well expressed, unless you look for them), and imbrication of the pebbles, which showed a northerly direction of current flow (from France?). The conglomerate is topped by a wind abraded platform (hence, the dreikanter). The yellow sandy horizon is interpreted as the basal aeolian sands of the Otter Sandstone Formation. All quite simple really......

These revelations brought our Geoliday week to a close. A simple 'Thank You Roger' on the beach at Budleigh Salterton was never going to be enough for the fine week we had all enjoyed. Roger, we hope our efforts in the field didn't disappoint you too much. Should you ever wish to lead another week in the field, we will all be in the queue to join. Thank you enormously. (Roger blushes hugely - 'The week was total pleasure for me and I enjoyed all your company and our discussions together immensely.')

Patricia Taylor, Terri Hudson, Tom Miller

NOTE: Copies of field notes for many WH Branch trips are held in the branch library, and can be supplied by request @ 5p per sheet. Enquiries and SAE to librarian.