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Hartley lies on the dipslope of the North Downs, as part of the chalklands which extend over much of southern England from the Humber to Dorset. The relief map below shows it slopes gently northwards and is surrounded
on three sides with the dry valleys of Fawkham Valley, Longfield
Valley and Hartley Bottom, but how has this come about?
Relief Map of Hartley, Longfield and surrounding area. Heights are
in feet above sea level, the axes are the OS grid references.
(Key: A - Hartley
Bottom Farm; B - All Saints' Church; C - Springcroft; D - Hartley
Green; E - Pennis House; F - Fawkham Church; G - Longfield Church).
The rocks that underlie our feet were laid down in the Cretaceous period (about 140-60 million years BC) when all this area was under water millions of years ago. First the area formed part of a freshwater lake where the Wealden sand and clay were laid down. Then the sea advanced, creating deposits of first Greensand and finally chalk. Chalk is a fine limestone probably derived from shells. Within the chalk are beds of flints - a hard silica from the skeletons of sponges.
The land was folded upwards into a dome, at the same time as the mountains of the Alps were formed. Later in the Eocene period the sea advanced again over north Kent and as far as Kingston in Surrey, and laid down new sedimentary rocks, the most important being London Clay - a soft rock that made tunnelling for the Underground relatively straightforward.
Older residents will say "The only thing that grows in Hartley are flints" - a reference to the layer of clay with flints that tops the chalk here and in much of the North Downs dip slope. It is thought to have been formed by the mixing up of Eocene deposits with the solution of chalk which left the flints.
Over countless centuries the work of rivers has eroded the weaker clays, leaving the harder Sandstone and Chalk as the higher ground with deep valleys where the rivers Darent and Medway have broken through the chalk.
In Kent and Sussex the Wealden Sandstones make up the land around Hastings and the Ashdown Forest. Then comes the band of level land on the clay, which includes the land around Tonbridge and Headcorn. The Lower Greensand forms a small ridge, the towns of Sevenoaks and Maidstone stand on this rock. The Greensand ridge is the source of Kent's best known building stone - Kentish Ragstone, a hard blue white limestone which has been used extensively since Roman times. It was used in buildings as diverse as churches, Rochester Castle, Knole House and Teston Bridge. Clifton-Taylor (English Stone Building) says it is a difficult stone to cut and it harbours dirt easily, and that "unfortunately" it was used by Victorian Church architects because it was cheap.
After a thin band of clay and upper greensand, we reach the chalk, which towers above the Weald in a striking escarpment, a testament to the relative strengths of the rocks. However the chalk is not itself uniform, at the base of the main escarpment of upper chalk there is a minor scarp of weaker chalk, and it is this layer that the Pilgrims Way follows.
The chalk of the North Downs dips gently towards the north, reflecting the geology that underlies our feet. A distinctive feature are the many dry valleys, where rivers once flowed. They can be seen locally in Hartley Bottom, Springcroft, Fawkham Valley Road, Pennis,
Hoselands Hill and Longfield. There are two theories as to how they were made, the first that the water table was once much higher, while the other is that during the ice age this area had tundra like conditions. The normally permeable chalk would have been made impervious by permafrost, thus allowing rivers to flow.
The chalk is not used very much locally as a building stone, but has been extensively mined for liming the acid clay soils. A field on the west side of Ash Road near Chapelwood was called "Limekillcroft" as early as 1590. Dene Holes for mining the chalk have been found at Cherry Trees, Northfield (previously called Pitfield), Manor Drive and Church Road, while up until quite recently there was a large quarry in the Wellfield Area, commemorated in the Pitfield road name. A 16th century coroner's inquest for Crockenhill shows that it was quite often women who went down the shaft with their baskets to collect the chalk stones.
The clay has been used for brickmaking, while the flints have been used both as a building stone for local churches, and up to about 50 years ago as a roadstone. According to Sherlock (British Regional Geology, 1947) they had to be the ones from the clay with flints which were hard wearing and rounded. Those taken direct from the chalk are too brittle and sharp.
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