OUGS visit to Samphire Hoe

17th August 2014

The and how the spoil at the foot of the cliffs is managed. How Chalk and flint are formed. How the channel developed.

Leaders:

Les Richmond, local geological and historical guide. Melanie Wrigley, ranger with the White Cliffs Countryside Partnership.

Rain hung in the air and the visit played out under a grey gloomy sky. A south easterly wind channelled the clouds along the coast and thankfully kept the rain away. The rain held off until our return journey back to Canterbury!

Location

Figure 1 - Samphire Hoe seen from the air. The A20 coast road to along the cliff top and Shakespeare cliff in the foreground. (Courtesy of Echo)

Samphire Hoe lies off the A20 between the ports of Dover and Folkestone. Specifically map reference 06’ 17.32N and 16’31.9” E. Access to the site is by a steeply descending tunnel dug through the chalk. This portal pierces Shakespeare cliff and serves as a permanent reminder of an attempt to drive a tunnel to France during the 70’s. The tunnel exit meets a ramp that runs to the base of Shakespeare Cliff and the Samphire Hoe plateau. Along the eastern edge of the plateau lies a 5 hectare industrial area housing several blue grey buildings. Fenced off and secure, they contain the ventilation and the cooling plant that pumps cooled fresh air into the channel tunnel. The Channel Tunnel is 50.5km long, and is the second longest tunnel in the world. The 37.4km midsection that runs under the sea, retains the record for the longest underwater tunnel in the world.

Samphire road continues on between low hills and terminates at a vehicle car park with three small buildings. The site is owned by the Eurotunnel plc. , and is managed by the White Cliffs Countryside Partnership on their behalf. The Samphire Hoe Country Park is open daily, from 7 am until dusk. Figure 2 - Ready for the off! We assemble at the coach park and greet our guides

With over 40 OUGS participants on this visit, we were split into two groups and having donned our hard hats were asked to wait by a grey van duly opened by the first of our guides - Melanie Wrigley.

The Naming of Samphire Hoe

The name Samphire Hoe was chosen as a result of a competition run by the local paper, the Dover Express.

Familiar with Shakespeare’s play King Lear, Gillian Janaway, a teacher of English, entered the name Samphire Hoe for consideration by the judges with the following reasons.

In act 4 scene 6 Edgar guides Gloucester, his now blinded father, to believe that he is on top of a steep cliff near Dover. Edgar speaks the following words:

"There is a cliff whose high and bending head looks fearfully in the confined deep… The crows and choughs that wing the midway air scarce so gross as beetles; halfway down one that gathers samphire, dreadful trade!"

At the time that William Shakespeare was writing King Lear he was said to have travelled regularly through Dover. The first cliff buttress on the West side of Dover is still known as Shakespeare’s cliff.

The ‘samphire’ of the play is a yellow flowering rock plant with edible stems and leaves. It also is known as sea asparagus, sea fennel or crest marine (Crithmum maritimum). The plant that was being gathered still grows wild on the sea cliffs and rocky shores around Dover. Though scarce in this locality today, it can be sourced from Jersey or I am told, bought from fishmongers along the coast. Rock samphire is also available as a salty, ‘aromatic’ pickle, rich in Vitamin C. It can be added fresh to a spring salad or boiled as a green vegetable.

Figure 3 - Crithmum maritimum plant Figure 4 - Mrs. Gillian Janaway seated by rock samphire plant The Hoe part of Samphire Hoe means it is a promontory, a piece of land that juts out into the sea. We can instinctively feel that the name Samphire Hoe describes the location perfectly; a prosaic link that ties the present with this place’s past.

Some local history

The Railway; the origin of the Green Fall

A rail road runs smoothly along the base of the cliffs. Built in 1843, this line hugs the coast between Folkestone and Dover. During the build, both Shakespeare and Abbots cliffs were tunnelled through. In between these tunnels the chalk had slumped and there had been several dangerous falls of rock. That section was blasted on the 26th of January using 150 barrels of gunpowder. After this big bang, the rock rubble was cleared away and the chalk was levelled to make the first promontory below the cliffs. This platform covered about 6 hectares, at a height of about 16m Above Ordanace Datum (AOD). A new piece of England, that was to be called the Green Fall had been created.

The railway company built some houses for railway workers and during the 1940’s to the 1970’s an isolated community grew by the addition of a number of cottages and boat houses along the shore. The Green Fall could be accessed by the Shakespeare Cliff Halt private railway station or by descending the zigzag cliff path known as Aker’s steps west of Shakespeare cliff, or another zig zag path down Abbots Cliff, otherwise it was a boat trip or a long trudge along the shore. During the war years the MOD took over the area. Munitions were stored hereabouts and new coastal fortifications were constructed.

Today the railway continues to maintain the link between Folkestone and Dover but Shakespeare Cliff Halt Station has fallen out of use. It lies near the entrance ramp, forelorn, dilapidated and in a state of disrepair.

The Green Fall platform protected the cliffs and reduced the amount of erosion by the sea. In so doing it allowed plants to gain a foot hold. However, measurements indicate that weathering of the cliffs especially through freeze thaw continues and the force of gravity does the rest. The cliffs retreat inland. Measurements indicate that cliff faces retreat by as much as 0.1m per year. In the past, weathering and erosion have led to some spectacular cliff failures, with many slumps and falls. One such slump, to the west of the site, happened on 26 January 1988 and removed some 6000 cubic metres of chalk. Likewise, in 1912, 50,000 cubic metres of chalk fell into the sea. The latest recent rock fall in February of this year was on the western side of Abbots cliff and narrowly missed the railway line. Cracks at the top of the cliffs above Samphire Hoe are clearly visible from the ranger's office and could quite possibly be the next section of cliff to fail. About seven tonnes of rock will tumble down adding to the developing scree slope at the base of the cliff. Where there is little fore shore, erosion keeps the cliffs white by removing rock falls, never allowing the vegetation to gain a foot hold and the cliffs to green up. Tunnelling and mining the Green Fall - problems with politics and with local geology.

The Green Fall provided an accessible working platform, a base from which mining and tunnelling enterprises were able to operate.

Tunnelling

The dream of a tunnel link to France began to take shape when Sir Edward Watkin a railway entrepreneur initiated a test tunnel in 1880. His miners used a mining machine invented by Colonel Beaumont MP but came to use an improved pneumatic boring machine patented by Captain Thomas English to drive the longest tunnel section under the sea. The 2040yds long tunnel passed through the lower grey chalk 100 ft below the sea and on a heading towards the admiralty pier in Dover. The technology worked and the break through just needed funding. However fear of invasion via a tunnel caught the mood of the public and an opposition to the tunnel grew. Politics of the time thwarted the drive and determination of Sir Watkin’s venture. Digging had to finally stop in 1889 when a high court injunction was served ending this affair. This tunnel became known as the Beaumont tunnel because it’s construction was wrongly attributed in ‘The Engineer’ magazine to have been excavated by the tunnelling machine patented by Colonel Beaumont MP. This tunnel was in fact driven by a more efficient tunnel excavator patented by a Captain English. However once the name entered the public domain it stuck.

Mining at the Green Fall- (some mining geology)

Successful collieries in Belgium and France indicted that coal measures should also be found in Kent. Lying the closest to the continent, Shakespeare Colliery also known as Dover Colliery was an obvious place to begin a venture and became the first coal mine to open in Kent. Kent Coalfields Syndicate Ltd. was formed in 1896, to take over a number of undercapitalized mining ventures. Bore holes had proved the presence of several seams of coal at depth, the best a 4ft seam at 2172ft. In June of 1896, the No1 pit (The Brady) was sunk. A 17ft diameter shaft was dug by miners and soon passed through the Chalk, Chalk Marl and Gault Clay strata. In October it reached the Lower Greensand 366ft. The Lower Greensand is an artesian aquifer and its waters flooded the pit. All further work was halted until pumps could be installed. Once this shaft was pumped out then work was able to continue. However the Brady pit had to be abandoned at a depth of 520 feet due to an influx of running sand that damaged the pump’s seals. In the race to mine coal, even before the pumps were installed in the Brady pit, a second shaft was started in November 1897. This was the 20ft diameter Simpson shaft. All went well until at 303ft water flooded this pit. The shaft sinkers were using a 15 ft test bore to check ahead for water. Disaster struck once the impervious Gault Clay cap rock was pierced. The pressure of water in the aquifer was so great that a jet of water broke through into the pit. The water gushed in with such force and so rapidly that only six shaft sinkers could be rescued. The survivors were lifted out by a bucket attached to the winding engine. The eight that remained perished, all had drowned. Once the pumps had been installed and the bodies of those who died were recovered the search for Kent coal continued. In February 1898 another shaft was started over the test borehole to compensate for the loss of the Brady pit. Then at a depth of 310 feet an interconnecting tunnel was driven between the two pits to provide a lodgement for the pumps. The volume of water that had to be dealt with at a depth of 450 feet was relentless some 54,170 gallons (24.63 cubic meters) per hour. Of this, 1,100 gallons was top water percolating from the sea through the rubble that made up the platform. 27,810 gallons entered from the Greensand and Hastings beds, and 25,260 gallons came up the borehole from below. The prospect of dealing with artesian water from even deeper aquifers still lay ahead. Incoming water continued to slow progress, but whilst sinking the shafts a thick bed of ironstone was discovered. This increased the potential value of the mine and the ability of the owners to raise additional capital. Just as well, as costs of pumping continued to affect the business. After refinancing the Company, and with changes to the management of the mine, the shaft sinking was once again able to go ahead. However the influx of water from depths stopped the sinking before the coal bearing measures could be reached. Then in 1902 cast iron walls were used to line the shaft and hold back the water. This is a process called tubbing. Tubbing the shaft allowed the shaft sinking to continue. The Simpson pit was also tubbed and pumped out. Both pits descended to a depth of 1632 feet (497m). The first coal seam was hit on 25 September 1903 but the coal seam was of poor quality with much shale. By 1907 the colliery was producing about 8 tons of coal a day but this was less than the colliery needed to raise the steam for its pumping and winding engines. The rich 4ft coal seams still lay 540 ft (165m) below. In 1907, Leney’s Phoenix Brewery in Dover purchased the first commercial coal from this pit and advertised their Dover Pale Ale as ‘brewed by Kent Coal’. They quietly dropped the slogan soon after. In 1909 the colliery was placed in the hands of the receiver and coal production ceased. Mining work re started in 1910 but the colliery closed in 1915, this time for good. Only around 1000 tons of coal had been mined and extracted. This had been poor return on investment. In 1918 the colliery was sold for the scrap value of its equipment. The mining waste from the colliery much of it Carboniferous shale was tipped and extended the edge of the Green Fall where it entered the sea at slump that had a 40 degree slope.

Figure 5 - Dover Colliery at Shakespeare Cliff (Images courtesy of Dover Museum CHIK Project)

Samphire Hoe

Samphire Hoe is the latest addition to the coast line of Kent. It abuts the Green Fall along its entire northern edge. The colliery and dwellings were demolished during its construction. A 1.7 km seawall, a barrier of piled concrete blocks keeps the sea away. The 1.5 metre wide wall is made up to a height of 7m Above Ordnance Datum (AOD). The sea wall is capped with a 1.2m wide wave wall to keep the sea at bay. Behind the wave wall extends a 13.5m wide flight of concrete steps capped by a concave sea wall. These are designed to dissipate the energy of storm waves that crash over the wave wall. The steps raise the height of the sea defence to 8.5m AOD. Grassed block work or ‘reinforced' grass increase the platform profile further still, up to an average height of 16 m AOD. In addition a bed of large rocks protect the base of the sea wall from the scouring action of high tides and rough seas.

Figure 6 - Channel tunnel construction and Figure 7 - Map showing the exposed geology of the Weald- the source of the rock infill. Artois anticline in England and France.

The development of the

The South-East of England and the North-West of France were once joined by the Weald – Artois anticline also called the Weald-Boulonnais anticline. The area experienced uplift during the late Oligocene to the middle Miocece when the syncline into which the Cretaceous and Eocene deposits had accumulated, were pushed up above sea level to create a land bridge that linked England with France. From then on the anticline was subject to erosion processes that created the basins of the Weald in England and the Boulonnais in France. The rock strata continue to run below the sea and these link England to France.

The Channel cuts the anticline and the story of its creation is hidden below the ground and under the sea. It covers a period of about 500,000 years. It includes two periods of glaciation, a number of changes in sea levels and a braided Channel River that drained the land masses of England and of France.

The first glaciation occurred some 450 000 – 425 000 years ago and known as the Anglian/Elsterian glaciation that covered most of Europe. As the climate grew warmer a vast glacial lake developed held back by the Weald-Boulonnais anticline. The elevated lake was fed by melt waters from the receding ice sheet, and the rivers Thames, Rhine and Meuse. Trapped and with nowhere to drain to, the lake’s level continued to rise by an estimated 25 -30 metres above the then current sea level. Eventually the lake’s waters overtopped the anticline at a low point somewhere between Dover and Calais. The release of the glacial waters would have rapidly eroded the chalk strata and created the first breach in the anticline. This mega flood of water overwhelmed and altered the drainage patterns of the rivers that fed the Channel river drainage basin. The Thames and the Scheldt were now able to connect and feed into the Channel river drainage system. The Channel river system carried an enormous volume of water. Major tributaries included the Solent river, the River Somme and the river Seine and fed its south easterly flow. This seems to have continued during the warm Hoxnian period and would have continued for the next 180 000 years. Despite the initial breaching of the Weald-Artois anticline the rivers Meuse and the Rhine continued to drain northwards into a northern sea.

The next dramatic development occurred during the Saalian/Woolstonian glaciation, about 200 000 to 120 000 years ago. Sea levels dropped as the glacier locked up the waters as an ice sheet. Once again when warmer times returned a glacial lake formed behind the breached Weald–Artois anticline. However this lakes shore line now lay north of the straits of Dover. Its level was lower and in addition to melt water from the ice sheet it was fed by the diverted rivers Meuse and Rhine as well as the Weser and the Elbe. Once again a gigantic fresh water lake that stretched into the Netherlands built up behind a somewhat diminished anticline. The anticline must have continued to rise after the Anglian/Elstrian breech to explain the new shore line being located further north. The Weald –Artois anticline was still experiencing compressive forces linked to the alpine orogeny. In addition the kilometre thick Saalian/Wolstonian ice sheet would have depressed the land over which it lay and that produce an uplift of the crust involving the Weald- Artois anticline north east of the of the Straits of Dover. The retaining barrier seemed to be of the weaker Gault clay and a breach in this barrier released the trapped waters and triggered yet another flood a second mega flood. Sonar scans reveal long ridges and gouged deep valleys that run parallel to the sides of the English channel. Flood markers indicate that the direction of flow was from east to west. There are v- shaped scours that taper upstream, streamlined islands, and the ancient Solent channel/river confluence now ends abruptly as a hanging valley anomaly. The expected V shaped point of juncture with the Channel river must have been eroded, cut away by a torrent that surged in the river valley below. Deep scours are found near the French coast as the flood was deflected by the elevated French coast creating scouring rip currents and eddies in its wake. These torn and scoured detritus were carried seaward and came to be deposited as sediments in the area of the Western Approaches where deltaic rivulets and fans appear.

Now as to the causes of the floods, they remain matters of speculation and debate. Overtopping through a col or by the back cutting of a bourne or stream from the western side of the anticline are all in the frame. Intriguingly movement along the edge of the old Avalonian microcraton along the Varingian Fault have been recorded during the past 1000 years and seismic activity should not be excluded. An old Varingian Fault line runs in the Dover Straits area in deep strata. In 1382 and again in 1580 sizable Earth quakes (an estimated 5.8 on the Richter scale for the one in 1580) occurred, with some loss of life. The earthquakes took place in the upper crust that caused houses, churches and castle walls to fall. The quake caused tsunamis and flooding in the region. Judging by the area of devastation they caused, the quakes had focal depths in the region of 20km or deeper. Tsunamis in the glacial lakes may have initiated the overtopping of the Weald-Artois barriers that then surged as the waters of the glacial lakes drained towards the sea. Much of the evidence for where the breaches occurred has been carried away and remains shrouded in mystery.

Once formed the channel cut off Britain from the continent and re-establishing that link is the next part of this story.

The channel tunnel geology

The channel tunnel runs through the Cretaceous rocks that form the anticline’s northern flank. The rock strata are more folded in France especially by the Sangatte-Quenocs anticline and fold. Associated with the Sangatte-Quennocs fold are a number of smaller anticlinal folds that ripple towards Kent. The subtleties of the anticlines geology are part of the complex interactions between the African- Arabian and Eurasian plates that occurred over a period of some 50 million years that created a system of connected yet discrete orogenic belts in Africa and Europe. The formation of the Weald- Boulonnais anticline is contemporaneous with the formation of the Pyrenees and the Alps and tectonic movements that helped to create them. Thrust faults are also located in this zone; some have 12m displacements that contact the sea bed. In the Sangatte area the strata are the most highly cracked and fissured due to the reactivation of faults that developed during the Jurassic or earlier. Angles of dip in the fold can be up to 20 degrees and faults that can have 15m displacements. These strata are not water tight and store large amounts of subterranean water. Tunnelling from France needed to keep the water out and this was solved by specialized High Pressure Balance Tunnel Boring Machines. These could tunnel with up to 10 atmospheres over pressures when needed. In the French section of the tunnel linings were made from bolted cast-iron and special high strength concrete and the junctions were sealed using neoprene rubber and grout (Anderson & Roskrow, 1994).

”Le Tunnel sous la Manche “ first broke into the flinty White chalk formation of the Lower Senonian (Santonian and Coniacian epochs) It proceeded on down to the Turonian Grey chalks and then onto the widening band of the Craie bleue or Chalk Marls of the Cenomanian. It is the lower levels of the Chalk Marls that then form the main horizon through which the tunnel passes through , all the way right up to its UK portal at Dollands Moor.

The mined rubble infill of Samphire Hoe is made up of the Cenomainian Chalk Marl from the UK side of the tunnel. On the British side the Chalk Marl bed is remarkably uniform and the Chalk marl bed is much thicker and gradually narrows as it approaches France. There were fewer faults on the British side in the Chalk Marl strata and where they occur they have offsets of less than 2 metres. The clay Marl beds have gentle angles of dip in the order of 2 degrees. Chalk Marls carry the channel tunnel for about 85% of the tunnel’s length.

The channel tunnel lies between 30 and 75 metres below the sea floor at an average depth of 50 metres! The tunnel does not follow a straight line. It was driven as far north as possible to avoid the mid channel Fosse Dangaered rubble filled ancient river valley that scoured the channel floor. Its mid channel position and great depth could have caused the tunnellers difficulties. Nevertheless a deeply scoured tributary of the Fosse Dangaered river valley could not be avoided and greater care had to be taken to safely negotiate this section.

Figure 8 – A simplified geological profile showing the channel tunnel (Courtesy of Tunnel Talk)

Mining the Chalk Marl

Chalk Marl is impervious to water, an important property when tunnelling under the sea. Chalk Marl also has good mechanical qualities under compression which are helpful in providing support during tunnel construction. The tunnel is not completely dry. There is some seepage of sea water in the English section due to the chosen method of construction but it is lower than planned for and lower than predicted. Seepage water is collected in three gravity fed sumps under the sea of which only one is being used at present. The water is then pumped to the surface where it is treated prior to discharge. Tunnelling through the deeper lower Gault clay stratum would have been even more problematical because it has less favourable properties and potential for swelling and distortion when wet. Such potential breaches can occur along fault lines.

The infilling of the empty lagoons at Samphire Hoe with Chalk Marl kept the amount of construction traffic movement to a minimum and to a large part solved the problem of what to do with the mined tunnel waste. Samphire Hoe contains 4/5ths of the mined spoil from the British side of the tunnel excavation. Figure 9 – Lagoon infilling at Samphire Hoe

The remaining 1/5th was used in the construction of the Folkestone terminal, 8 km distance from the undersea tunnels at Shakespeare Cliff. The Folkestone Terminal covers 150 hectares. Its construction had an initial need to stabilise the site in order to prevent the sides of the adjacent escarpment from subsiding. The level of the whole site was then raised to level up to the surface soils and to reduce the steep inclines.

When tunnel construction was completed in 1992 the Samphire Hoe site already had the ventilation and cooling facilities in place. In October 1993 the remaining site was landscaped to provide a series of gently sloping hills and valleys. Ponds were added to create a wet land in the west. The waters drain into the sea through a sluice gate in the west.

Chalk Marl soils

The composition of the chalk marl varies being made from between 60-70% chalk and 30-40% clay in its lower levels. I am told that a 60:40 mix is ideal for making Portland cement a helpful reminder of that Chalk Marls also found in Dorset. Samples of Chalk Marl from Samphire Hoe comprised 10% quartz, 30% smectite and 60% calcite and may have come from the upper Chalk Marl layer. Chalk marl soils are alkaline and high in calcium and a typical pH range of 7.1 -8.0. Calcium loving plants are called calcicoles and form plant communities that are able to tolerate these conditions. The clay content within the Chalk marls makes the soils more productive as more potassium is available. However analysis of the pH of Chalk Marls from the Tunnel borings showed that they had a tenfold increase in alkalinity with a pH value of 9.3. The Chalk Marl had very little available phosphorus (zero on the ADAS scale (Ministry of Agriculture, etc., 1973)), moderate amounts of potassium (ADAS index 3), large amounts of magnesium (ADAS index 7), and again virtually no nitrogen.

Typical plant cover on a farmed Chalk Marl is as a pasture that is established on a rendzina type soil. Rendzinas are thin soil that are well drained and have a shallow upper most band enriched by organic matter. They are nutrient-poor soils, high in calcium carbonate that comes from the underlying rock. Such soils dry out quickly and being shallow subject the plants to periods of water stress and droughts. The communities of plants and animals that colonise rendzinas are specialists and the plant communities are quite unique.

The creation of a natural plant community at Samphire Hoe would therefore present quite a challenge. The Flora

Pioneer plant species were collected from ‘The Folkestone Warren’ and cliffs. The Warren is a coastal area east of Folkestone and a designated SSSI. Twelve cliff slumps have occurred here since 1765. These slumps run into the sea as a series of successive bands of softer Gault Clays overridden by more durable Chalks. Water pools in the hollows to form ponds and over time has produced a unique habitat that overlies a remarkable geology. Staff from Wye College gathered seeds from the Warren and increased this seed stock to enable the seeding of (Lotus corniculatus), buck’s horn plantain (Plantago coronopus), chalk milkwort (Polygola calcarea), colts foot (Tusilago farfarra), common kidney vetch (Anthyllis vulneraria), common rock rose (Helianthemum nummularium), cow slip (Primula veris), fairy flax ( Linum catharticum), false dandelion (Hypochaeris radicata), hedge bed straw (Gallium mollugo), hoary plantain (Plantago media), meadow goat’s beard (Tragopogon pratensis), pidgeon scabious (Scabiosa columbaria), rib wort plantain (Plantago lanceolata), rough hawksbit (Leontodon hispidus), salad burnet (Sanguisorba minor) and wild thyme (Thymus praecox). Stinking iris (Iris foetidissima) occupies a niche at the base of the cliffs. The seed mixtures reportedly contained 31 species in all. Rye grass (Lolium perenne) was used to colonise the middle area, to develop a grass cover quickly. The wet lands were left unseeded to be colonised naturally.

The vegetation development has gone through three phases.

• After the initial sowing it took at least five years for the grassland to develop significantly.

• In the second phase the sown areas became well vegetated and rest harrow (Ononis repens) became super abundant.

• The third phase is the arrival of woody species, the orange fruiting sea buckthorn (Rhamnus catharticus), blackberry bearing bramble (Rubus fruticosus), may flowering and red berried hawthorn (Crataegus mongyna) and white flowering and red berried wayfarer tree (Viburnum lanata).

Also the unsown areas are also developing a full cover of vegetation.

To establish a chalk grassland pasture community grazing by farm livestock has been introduced. In 2003 the first grazing took place using a very low number of sheep in small electric fence enclosures. In 2004 the site was entered into the DEFRA funded Countryside Stewardship and sheep numbers increased to 40+. In 2008 the Hoe was entered into High Level Stewardship and a permanent perimeter fence was established. In the autumn cattle grazing was introduced (6) concurrently with sheep grazing (40+). In the winter of 2010 some areas of grassland were strimmed and the cuttings removed. Woody regrowth is being chemically treated with ’Roundup’ a glyphosphate herbicide and Triptic 48 EC a tryclopyr selective herbicide that kills broadleaved species. The down side is that both herbicides remain in the soil for some time and Triptic retains its toxicity in the aquatic environment. Unwanted wind dispersed colonisers such as spear thistle (Cirsium vulgare), creeping thistle (Cirsium arvense) and ragwort (Senecio jacobaea) are cut, sprayed or are pulled. Ragwort is highly toxic to horses, cattle and chickens but can be tolerated by sheep provided its intake remains small.

The mass of rest harrow (Ononis repens) remains a challenge, as a nitrogen fixing plant with Rhizobium nitrogen fixing bacteria in its root nodules it enriches the soil which allows some of the rougher grasses to take hold. Sainfoin a leguminous forage plant was also seeded in order to improve the nitrogen content of the soil. However its numbers remain low being selectively grazed by wild and domestic herbivores.

There can be conflicts between managing for short and long pasture grass species.

Over 200 plant species have now been recorded on this site. The monocotyledonous grasses are typical of those found in chalk meadows and include the following, cocks foot (Dactylis glomerata), crested hair grass (Koelaria marcantha), heath false brome (Brachypodium pinnatum),meadow goat’s beard (Tragopogon pratensis), meadow oat grass (Avenula pratensis), quaking grass (Brizia media), red fescue (Festuca rubra), sheeps fecue (Festuca ovina), tall fescue (Festuca aurundinaceus) . Sedges include the glaucous sedge (Carex flacca). Flowering plants include those typically found growing on chalk marls, such as bird’s foot trefoil (Lotus corniculatus), buck’s horn plantain (Plantago coronopus), chalk milkwort (Polygola calcarea), colts foot (Tusilago farfarra), common kidney vetch (Anthyllis vulneraria), common rock rose (Helianthemum nummularium), cow slip (Primula veris), fairy flax ( Linum catharticum), false dandelion (Hypochaeris radicata), hedge bed straw (Gallium mollugo), hoary plantain (Plantago media), meadow goat’s beard (Tragopogon pratensis), pidgeon scabious (Scabiosa columbaria), rib wort plantain (Plantago lanceolata), rough hawksbit (Leontodon hispidus), salad burnet (Sanguisorba minor) and wild thyme, (Thymus praecox). Stinking iris, (Iris foetidissima) occupies a niche at the base of the cliffs.

A measure of the success of the scarce plants is the number of orchids that grow at Samphire Hoe. Both pyramidal and common spotted orchid occur here in patches. The colonization of the site by early spider orchids (Ophyris sphegloides) is remarkable. Around 8,500 were counted in 2013, and 10300 in 2014 with a record of 12399 in 2004. The population numbers appear to fluctuate and may possibly reflect the time of counting. Samphire Hoe is now an important site for this species.

Figure 10 – Samphire Hoe early spider orchids

Maritime dicotyledonous colonizers now include; buck’s horn plantain (Plantago coronopus), golden samphire (Limbardia crithmoides), greater sea spurrey (Spergulari media), lesser sea-spurrey ( Spergularia marina), Nottingham catchfly (Silene nutans), rock samphire (Crithemum maritimum), saltbush (Atriplex halimus), rock lavender ( Limonium binervosm), sea beet ( Brassica oleracea var maritima), sea carrot (Daucus carota), sea cabbage (Brassica oleracea), sea lavender (Limonium vulgare) and wild common madder (Rubia peregrina ). All these plants are able to tolerate salt splashed areas close to the sea wall. Rock Samphire now even colonizes the cracks and crevices on the western parts of the sea wall.

Woody shrubs such as sea buckthorn (Hippophae rhamnoides), hawthorn (Crataegus monogyna), wayfaring tree (Viburnum lanata) and wild privet ( Ligustrum vulgare) have established themselves and provide some shelter from the prevailing winds.

A study on the colonization of the site by arbuscular mycorrhizal fungi AMF showed that plants forming mycchorizal associations fared better than those that did not. 12 species of AMF were identified on the site.

The fauna associated with the flora

30 Chalk grassland butterflies have been counted including the wall brown (Lasiommata megera) and the heath (Coenonympha pamphilus). About 170 species of moth, including 5 featured in the Biodiversity Action Plan have been seen on the site. 13 species of dragonflies and damselflies frequent the ponds.

Reptiles such as common lizard (Lacerta vivipara), slow worms (Anguis fragilis), and adders (Vipra berus) have been encouraged to inhabit a strip of fenced off scrub between the south facing cliffs, the railway and the grazed grassland and may be seen warming in the morning sun.

140 species of birds were recorded in 2012, of which 16 species bred in the area excluding the breeding of 6 species just beyond the recording area. Peregrine falcons and house martins nest in the cliffs above the Hoe.

The park has gained some mammalian colonizers also. Pigmy shrew, bank voles, common shrews, wood mice, hedgehogs, rabbits, badgers and foxes are now considered as visitors or colonisers.

The Folkestone Warren a wild coastal SSSI some distance away to the east and downwind from the prevailing south westerly’s is a likely source of wind carried colonisers and the strip of railway land a potential wild life corridor between the two sites. It also acts as a dispersal corridor for ragwort.

The Geology

During our visit we were able to cover the following:

• The Chalk Marl infill, • The chalk cliffs • The fossils found in this locality.

The site also offers an opportunity for ecologists to study plant succession and diversity. The site now boasts in excess of 200 plant species and numerous animal residents and visitors.

The Chalk Marl infill

Chalk Marl is made up of repeating bands of alternating clayey chalk and limestone without flint. The Chalk Marl deposit has now been undergoing the processes of weathering and soil formation over a period of some twenty years. In places in particular on north facing slopes the soil is still very thin and occasional stony fragments of Chalk Marl break through. These were the ones I picked up and examined.

Chalk Marl at Samphire Hoe is reported to contain small fossils which have been fragmented by the tunnel boring machinery. It is also reported that fossils can be found after long and careful observations of the Chalk Marl infill. Work on micro fossil foraminifera was carried out by Eurotunnel and the changes in their type and number of the foraminifera has led them to conclude that the formation of the Chalk Marl horizons was due to tectonic forces producing changes in deeps and shallows in the beds rather than the effects of Earth orbit forced cycles.

I was unable to find any large fossils in the few fragments I looked at.

I chose to examine rock samples that broke through the thin soils on the northern sides of the hills near to the path as we progressed east. This obviated the need to disturb the grassland ecology or the soil. All rocks had a distinctive buff colour, a slight laminar structure and a sub conchoidal fracture along the lightly laminar compressive plane. Under a 10x loupe, the buff chalk clay matrix contains a slight peppering of irregular dark inclusions of a greenish black material probably glauconite at around a 5% concentration, that showed of a wide range of sizes 0.2 mm to much less and the occasional shiny clear, transparent, micro-crystalline faces that are highly reflective and are likely to be quartz. At concentration level of 1% or less. The rock cannot be scratched by a finger nail, it is just scratched by a copper coin and easily scratched by steel giving it a value of around 3 on the Mohs Scale of hardness. It made an ‘off white chalky streak’ on the streak plate. It also produces an effervescent fizz when treated with a drop of citric acid. (Citric acid is crystalline and can be made into a solution in the field with a drop of water and so is easier to carry than a bottle of hydrochloric acid). The rock does seem to be impervious to water and is not slippery when wet but an abrasive feel.

These properties have more in common with a more durable limestone band in the Chalk Marl than the general properties of a 30% clay Chalk Marl deposit. Unwittingly my sampling method appears to have been selective for the former. The geology of the chalk cliffs

Samphire Hoe is a good starting point to study the Chalk of the Folkestone to Dover section and forms part of the standard British successions. Unfortunately due to a rock fall, the Aker's Steps path on the cliff, at the eastern end of Samphire Hoe, is unsafe and unusable. A geologists equivalent to the ‘samphire foragers’ view of the chalk, ‘white up close and personal’ was not possible today and had to be put off until this cliff path is made safe again.

The cliffs are impressive – massive buttresses of white, patched with green vegetation (the Green Fall), and soar 100 metres into the air.

Melanie our guide began her talk with a description of how this chalk was formed.

Chalk is made up of micron sized coccoliths, intricate plates of calcite that may be shed as individual plates by coccolithophores (types of marine phytoplanktonic algae).When coccoliths cover the whole of the algal cell they make a sphere , an exquisite filigree of calcite that envelopes the cell, that’s called a coccosphere. As coccolithophores grow and bloom, plates and spheres of calcitic biomicrite rain down and cover the sea bed. Chalk accumulates on the sea floor provided it is deposited above its Carbonate Compensation Depth, a depth at which it dissolves back into the sea. In the Oceans of today calcite is soluble in cold waters at depths below 5000 -3500 metres. The aragonite form of carbonate found in shells dissolves in depths that are shallower still. It is generally considered that the coccoliths that made up these chalks were deposited in warm shallow seas with temperatures of about 20 degrees Celsius. Those furthest away from shore were the least contaminated by material transported from land produce the purest and whitest chalks. During the Cretaceous, chalk locked up vast tonnages of carbon dioxide in the form of these carbonate rich sediments. This in turn reduced the amount of carbon dioxide gas available for recycling both in the atmosphere and the sea. This reduction of this greenhouse gas preceded a period of cooling in the late Cretaceous and is of interest today.

Figure 11 - SEM coccolith and coccosphere made by Emiliania huxleyi. (Source Natural History Museum)

Access to these cliff faces is blocked by the rail line a wire fence protecting the railway line and a wooden and barbed wire fence along the path so the chalk has to be observed from a distance. A good pair of binoculars was a handy piece of kit to have.

The cliff stratigraphy

Chalk is non uniform with recent changes in its stratigraphy and divisions. Currently the BGS divides the Chalk of the Upper Cretaceous into the White chalk (Upper) and Grey chalk (Lower) groups.

White Chalk has a wide variety of materials within it and these help to identify the strata which have been given a variety of names. Perhaps the easiest to distinguish are the bands of flint within the chalk near the cliff tops that belong to the Lewes Nodular chalks. The flints are irregular in shape and are made of silex derived from siliceous sponge spicules and skeletons of foraminifera. The silicate solutions were re- precipitated at an anaerobic redox boundary somewhere within the sediment to produce bands of flint.

Below these flinty chalks lies a zone of chalk free from flints, the New Pit chalk formation. There are thin conspicuous marl seams within the chalk that are used to characterise New Pit Chalk formation. Some of these marls were derived from the ash fall-out from volcanic eruptions. Others may be sedimentary in origin. The presence of iron in some layers was inferred from the rust coloured stains observed running down the cliff again from a few bands. These usually mark the presence of sponges.

Figure 12 - The fenced off chalk cliffs showing some of the stratification with the Hollywell nodular chalk at the lower levels.

Below these marly beds lies chalk with clearly discernible lumps the size of boulders. This chalk with these distinctive nodules belongs to the condensed Hollywell nodular chalk formation. This is a formation that has yielded Lower Turonian ammonites.

Below this group lies a series of distinct, thin, more grey than greenish clay bands that delimit the base of the White Chalk formation. These are the Plenus Marls. They can be examined more closely should you wish to go beyond the sea wall at the eastern end the Samphire Hoe platform, at the base of Shakespeare cliff and also on Aker’s steps. Almost a point of pilgrimage, a place that has been extensively studied by geologists.

The name Plenus Marl recalls its earlier name of Belemnite Marls. A series of distinctive clay bands containing numerous fossils of the large belemnite Actinocamax plenus associated with the upper parts of this layer. Here the Plenus Marls are about 1.5 metres thick, a quarter of the thickness of Plenus Marl beds found in locations further west. Despite the thinness of these sections, the 8 marker beds that characterize the Plenus Marl have been identified below Shakespeare Cliff.

The Plenus Marls mark the base of a major complex positive 13C excursion that extends into the basal part of the overlying beds. This is referred to as Oceanic Anoxic Event 2 (OAE2) or the Bonarelli event after the Italian geologist. This excursion is accompanied by a significant extinction attributed to increasing anoxic (low oxygen and anaerobic) conditions being present at the time of deposition. This was followed by a gradual recovery as higher oxygen levels returned the seas to more aerobic conditions. The OAE2, occurred at the Cenomanian/Turonian boundary (about 93.5 Mya). Based on recent osmium isotope analysis the OAE2 is thought to have been triggered by a massive magmatic event.

The Lower Chalk is quite distinctive because it is grey and flint free. The grey is due to its high clay content. This may reflect the lower sea-levels and magmatic events that were contemporaneous at the time of their deposition. The Grey Chalk is also made up of thin alternating cyclical clay rich darker bands and clay-poor whiter bands of chalk. The thin gritty, silty, chalk beds act as markers for the sequence. Some of the Grey Chalk clay bands are linked to vulcanism and have been identified through isotope marker horizons. This enabled similar marker beds to link hitherto unrelated grey chalk horizons. Only the upper Grey Chalk strata are visible at Samphire Hoe. Those beneath the Plenus Marls belong to the Zigzag chalk, the uppermost strata of the Grey group Chalk member.

Fossils

Fossils can be located on the coast to the east and west of Samphire Hoe and the Green Fall. Towards Dover to the east, the soft chalk cliffs are exposed to wave action and stay white with eroded slips, slumps and rock falls at the base of the cliffs. Towards the west and Folkestone lie the Grey Chalk subgroup and the fossils found in the Gault clays which are exposed at low tide east of Abbots cliff and the slumps of the Warren before Folkestone. Smaller boulders may also be carried towards Samphire Hoe from west to east by longshore drift that features along this part of the English Channel.

Melanie showed us a number of fossils from her collection. Two ammonite part spirals. The first specimen had narrow sinusoidal ribbing on the shell but was only partially visible. The second was a much heavier, more massive specimen that showed ribbing with raised tubercules. No sulcus mark was visible on either specimen. Melanie then compared these to a small nautilus shell in her possession and explained how this living relative of the ammonites is able to alter its buoyancy by controlling the amount of gas in the chambers within the shell; rising from the deep when it feeds on the plankton at night.

Pictures from top to bottom

Figure 13 - Melanie Wrigley introducing the ‘chalk talk’ about the site and about to present her fossil finds.

Figure 14 - An unusual find thought to be a manubrium of a medusoid jellyfish (a soft bodied invertebrate!)

Figure 15 - A molar tooth from a mammoth dredged up by a trawler working the channel.

She then showed us a fossil of an early echinoid Micraster (heart shaped echinoderm) that was preserved in a nodule of flint. Micraster was studied in this area by Arthur Rowe of Margate and published in 1899 his classic paper on continuous evolution. Micraster shows the progressive deepening of the sulcus (groove) during the Cretaceous. It is thought that this echinoid had a burrowing habit which offered it some protection from predators. An observable deepening of the sulcus was interpreted as a trend in Micraster evolution which enabled these echinoids to increase the flow of water into their burrows and thus obtain more food.

Starting above and going clockwise –

Figure 16 - Folkestone, and the beach at the west end of Samphire Hoe with lumps of Gault clays.

Figure 17 - The massive sea wall that protects Samphire Hoe looking east.

Figure 18 - Some of our group are talking about the ecology and where I saw my first sea cabbage. Dover harbour and White cliffs gleam in the top left corner against a grey and dismal sea.

Despite the gloomy weather, the trip was a great success. We all had the chance to discuss some geology in the field with colleagues. All were able to exercise our conference legs. The ozone rich sea air proved invigorating and I ..... , well, I also had a small piece of Chalk Marl limestone to add to the HBS science department rock collection.

Samphire Hoe is interesting because of the Cretaceous geology, its link with a modern wonder of the world. The Channel Tunnel and the unique Chalk Marl ecology it offers. Thank you, Kent OUGS for organising this visit. Dr. Zbig. Towalski