Industrial Geology of Kent & Sussex
Compared to other parts of the British Isles, the south east of England can be considered as comprising relatively uninteresting rocks such as chalk, flint, clays and gravels. This is the result of our stable geological heritage where for hundreds of millions of years, little to no volcanic or intense tectonic activity has taken place.
What volcanic activity may have occurred in the past happened far back in the Palaeozoic era and is now buried under Mesozoic and Caenozoic strata hundreds of metres thick.The only tectonic process to have visibly affected these counties is the rippling effect of Africaís collison with the European plate that formed the high alps of Italy, Austria and Switzerland. By the time it reached Englandís shores this effect had lost much of its power and all we see are the gently rolling hills of the North and South Downs.
The geological processes that gave counties to the North and West of England their deposits of lead, tin, copper and gold passed us by. However, despite this lack of the more valuable minerals man has, throughout history, made the best of what geology had to offer this part of the country.
The first mining activity in the south east of England was in the collection of the silicate mineral known as flint, a common substance found throughout the North and South chalk Downs and in many of the Wealden clays.
This was a valuable resource for prehistoric man, being easily chipped (flint breaks with a conchoidal fracture) it could be shaped to provide man with many useful tools such as axes, knives, scrapers, needles, spear heads etc.
Many flint implements have been found in the area, from Brooklands lake in Dartford and east along the Thames to Swanscombe - the site of Swanscombe Man.
|Flint implements are named after the period in which they were made and used:-|
Neolithic - later than 2500 BP
Mesolithic - 8000 to 2500 BP
Palaeolithic - 20,000 years BP
Mousterian - 100,000 years BP
Levalloisian - 200,000 years BP
Acheulian - 330,000 years BP
Clactonian - 450,000 years BP
Kentish stone has been used for building purposes since the neolithic period some 2,500 years ago. Kits Coty located between Chatham and Maidstone, is the remains of an ancient tomb. Once completely covered by an earthen mound, all that remains is the inner framework, formed from slabs of local sandstone.
Kentish Ragstone - a hard limestone found around the western Weald was used by the Romans to construct much of the wall round Londinium, and the Normans continued this trend in the building of the Tower of London.
Virtually all of the churches in the London suburbs are built from this grey/buff material. Many buildings around the south east have been constructed from local sandstones and Ardingley sandstone is still quarried today between Crowborough and Horsham, Sussex. A classic example using local building materials is Batemanís House, at Burwash, Sussex, once home to Rudyard Kipling, with its sandstone walls and grey limestone paving.
Batemanís House, originally built for a wealthy ironmaster is now owned by the National Trust and is open to the public every Saturday-Wednesday from April to October. Telephone 01435 882302 for details. Batemanís House, Burwash, Sussex
Knapped flint - flint nodules split so that one face is flat - cemented into a rough mortar has been extensively used throughout the ages for walling as can be seen from the photographs here of Dartfordís Parish church dating from 1080 (the white stone blocks visible are Tufa - a limestone rich in Calcium Carbonate) and an early 20th century house in Bexley.
A shell limestone comprised predominently of fossilised freshwater snails and known locally as Sussex Marble or Winkle Stone can be seen in the walls St Mildreds Church, Tenterden, Kent.
Until the development of coal fired blast furnaces in the early 18th century, the South East enjoyed a virtual monopoly on iron production in England, with major sites at Robertsbridge, Battle and Wadhurst in Sussex and Lamberhurst in Kent.
The pits, kilns and charcoal workings themselves are now all long gone but a lasting product of these mines can still be seen today in the railings around St Paulís cathedral in central London.
Sir Martin Frobisher, an Elizabethan seaman who sailed with Drake and Hawkins against the Spanish Armada, made three voyages in search of a north-west passage through the Americas to India and China.
His ship, The Gabriel was a 20 ton Barque, built in one of the Thames shipyards specially for Frobisher's first voyagfe to Canada. Frobisher set sail from Ratcliffe Cross, near Limehouse.
He did not succeed in this, only finding what is now known as Frobisherís Bay in northeastern Canada, but his expeditions did leave Kent with an unusual geological legacy.
He discovered a rock '...black as a seacoal but heavy like a metal...' that he was told by an assay office in London contained gold.He made two further voyages. In 1578 he brought back 160 tons of rock and in 1579, having taken over a hundred Cornish and Dorset miners with him, brought back an additional 1200 tons.
This ore was brought to Dartford to be crushed at the local powder mills alongside the river Darent and special furnaces were constructed to smelt the ore and recover the gold. No gold was found and only £100 worth of base metals were recovered from the ore, a sum far less than the cost of the expeditions to mine it. The stone was dumped and much subsequently used to construct the perimeter wall around Dartford Priory, where it can still be seen today.
Given that the geology of Kent and Sussex is made up almost exclusively of Cretaceous strata, it is surprising that coal features in the landscape at all. It should however be remembered that an almost complete succession of strata dating back to the early Palaeozoic do underly the rocks so familiar in these counties, albeit sometimes at great depth.
A borehole made at Dover in 1890 proved that coal did exist at a workable depth and the first colliery, the Shakespeare, was opened in 1896. It produced little economic coal and soon closed. Following further geological surveys of the area however, four other pits were started over the years in east Kent, Tilmanstone, Snowdown, Betteshanger and Chislet.
The depth of these ranged from 450 metres at Chislet to over 900 metres at Tilmanstone. The seams vary in thickness from a few centimetres to 3 metres and cover an area of over 600 square kilometres. At itís peak, these coalfields produced 1.5 million tonnes of coal a year, but in the 1980s, along with much of the rest of the coal industry in Britain, these pits were closed as increasing prices and a reduction in the market for coal made the working of these seams uneconomical.
After much controversy over the years as to what Deneholes were for, modern research has determined that they were a method of extracting chalk for use either as a fertiliser or top dressing to the fields above. Denehole mining has been in evidence in Kent since before Roman times, reaching itís peak around the 13th-14th centuries. The last known denehole was dug at Doddington, near Sittingbourne, during the years 1904 to 1908.
The Bexley and Dartford areas contain hundreds of these features although most have now been capped or filled in for safety reasons.Cross section of a denehole
From these small beginnings were to grow a major industry - the manufacture of cement - and the development of Portland cement in the mid-nineteenth century was to change the face of the south east.
Whereas the agricultural use of chalk depended upon leaving the topsoil levels undisturbed, the industrial requirement for chalk was to extract large amounts in the most cost effective method available, open cast mining.
Today, 2 million tons of chalk are mined annually from the North and South Downs, primarily from Lewes and Portslade in Sussex, Sittingbourne, Rochester and Dartford in Kent.
It is mixed in a 4:1 ratio with clay, baked to 1500ļ Celsius and then crushed to a powder. After the addition of 6% gypsum, this produces the cement used by todays construction industry in vast quantities. Chalk is also used as a filler for paper, paint rubber and plastics.
Concrete has two basic components, cement (see Chalk) and ballast, in the form of gravel.
River gravels are extensively mined at Sturry in the Stour Valley, at Dartford in the Darent Valley and at Aylesford and Leybourne in the Medway Valley. Marine shingle is also used as ballast and this is obtained from beach deposits at Hythe, Dungeness and Sandwich in Kent and from Rye and Eastbourne in Sussex.
Sand is extracted from Hythe, Borough Green, the Isle of Grain, Maidstone, and Canterbury in Kent and from the Hassocks area in Sussex. Seams of clay, laid down during the Jurassic and Cretaceous periods, form the raw material for the brick industry and working quarries still exist in Tonbridge, Westerham and Storrington in Kent and at Horsham and Danehill in Sussex.
Most Gypsum in the British Isles is found in Permian and Triassic sediments in the Midlands, Cumbria and Yorkshire but in 1873 gypsum deposits were discovered in Sussex in Jurassic Purbeck strata dating from the late Jurassic era, 135 million years ago.
These seams are composed of pure gypsum with no rock matrix or impurities and hence can be mined without any waste residue, or gangue to mar the landscape. The seams range from two to four metres thick.
Two mines exist, one at Brightling one at Mountfield and between them produce a quarter of the total gypsum mined in the United Kingdom.
Providence Resources plc
Offshore reserves of oil and gas have been known and recovered from the North Sea since the 1960s but surprisingly, England also has onshore fields twelve of which are currently in operation across Surrey, Hampshire and Sussex:Hampshire
An exploratory well at a thirteenth site, Leith Hill, Surrey, is currently being drilled.
Most of these sites lie on a geological feature called the Portsdown - Paris Plage Ridge that runs under the English Channel from the Hampshire Basin to Le Touquet in France.
Oil and gas have been found in strata ranging from the Great Oolite of the middle Jurassic to bituminous shales within the Lias of the lower Cretaceous.
How much of the geology of the south east continues to be worked will depend on Government policy at both national and local level and in market forces determining whether particular deposits can be worked economically.
Certainly, at the time of writing, there are literally billions of tons of rock, chalk, clay, sand & gravel remaining that could be developed further.
Perhaps as more easily obtained resources elsewhere are exhausted we may in the future see the re-opening of the Kent coalfields or a new renaissance for the Wealden iron industry. With advances in Earth resource surveying, mining methods and extraction technology, we may one day see the exploitation of the palaeozoic basement rocks beneath the south east. As these rocks were once subjected to the same tectonic forces that produced the important mineral rich strata that exist elsewhere in the country similar bounty may lie literally beneath our feet.