A brief description of the geology of Wye and Hinxhill

THE GEOLOGY OF WYE AND HINXHILL

Wye Geology – from National Geological Survey

We all appreciate the impressive beauty of our local countryside. Indeed its magic is marked by the title “Area of Outstanding Natural Beauty”. We are also fond of reminding ourselves and others that Wye has a very long history of human occupation. Perhaps we find even the passing of human generations difficult to comprehend and historical time gives some kind of reality to our present predicament. That geological time has more significance to the present than we dare to admit presents us with a dilemma. How can such vast reaches of time be more meaningful to our present views of history and beauty than the more recent written accounts?

For those of us who grew up with the writings of Dudley Stamp to inform our understanding of physical geology it is no surprise that landscape, in general, and the beauty of the North Downs owe so much to the passage of aeons. That the bold escarpment of the chalk Downs because of deep warm seas and that the chalk developed above the heavy grey clay that were once quarried in Naccolt is wonder enough. But to understand that the same geology gave rise to the same grazing qualities of the downland sward and the brick red walls of our beloved village gives cause to our anger and pride of last year.

 

A brief overview of the superficial geology of the British Isles may help us place our local geology into the wider context. Most of the country is covered by a fairly thin layer of soil which consists of a mixture of finely broken down minerals and organic matter. Beneath the soil and sometimes exposed at the surface are layers of rocks that were developed at varying depths beneath the Earth’s surface. These layers (strata) are tilted usually relative to the present day surface and exhibit a cross-section of the strata. It is a matter of great coincidence and importance that the oldest rock strata are found exposed in the west of the British Isles and the youngest in the east. On a geological map these bands or cross-sections run roughly from the south west to the north east. The significance of this is that the recent and softer rocks make up the gentler, more agricultural landscapes of the east and the harder, older rocks appear predominantly in the western, hilly and more rugged parts of our islands. Consequently many of our river systems start in the higher, older rocky areas and find their ways, along with much alluvium, onto lower plains. The sedimentary processes that have been part of our evolving landscape for millions of years are still continuing and it is this dynamic aspect of geological evolution that gives us opportunities to predict how our environment will change in the future.

 

 

The south east has been studied extensively and the present summary of the solid geology of Wye and Hinxhill borrows much   classic work of Paul Burnham and the excellent text by Bannister and Watt. Deep below the exposed rocks of Kent and Sussex are rocks that reach back to Palaeozoic era and the early (Triassic and Jurassic periods). These rocks have played a significant part in the subsequent shape and lithography of our region. In particular the transgression of several ancient seas laid down marine/shallow lake or littoral sediments that are sometimes quarried in the Weald. Originally these older layers of sand and clay were overlain by a thick layer of chalk deposited during the Cretaceous period (135 to 70 million years ago). At this time the North Sea floor was higher than it is now and when, about 100,000 years ago, the North Sea began to sink lower, the south east corner began to buckle upwards. This formed an upward convex region called an anticline. The centre of this exposed dome of chalk was probably severely strained and would have been liable to relatively high rates of erosion. Consequently, the central part was worn down to form what is now called the Weald. However, across the Weald the exposed strata experienced different rates of erosion because they present differing physical and chemical durability and so are featured as differing land heights. Thus the Hastings Beds – a hard form of sandstone – are found in the hillier part of the High Weald. Beside the High Weald the softer Weald Clay establishes the Low Weald. Next, towards the rim of chalk is the Slightly higher eponymous Greensand Ridge and closer still, forming the region called Holmsdale, is the sticky, grey, Gault Clay. Finally, rising magnificently around the edge of the Weald is the chalk. The chalk underlies most of the north and south east Kent plateau but there later sedimentary deposits have made for the rich and varied agricultural lands of Thanet and the north Kent coast.

 

The location of Wye is therefore at the foot of the scarp of the North Downs and interestingly at a fairly shallow crossing of the Great Stour. The system of the river Stour has contributed much to the local topology. Firstly it rises in the Weald as two tributaries – the East Stour and the Lesser Stour. At Ashford they merge and from then onwards the Great Stour has cut its way through the chalk of the North Downs. Paul Burnham has noted several faults locally in the vicinity of Wye and it is reasonable to suppose that during its geological history the Great Stour took advantage of such a fault and pursued a path that cut across the Downs. However, the story of the Great Stour during its 100,000 year history is also wonderful. It was once a tributary of the Thames and met that river system, which flowed west to east in a periglacial region, near present-day Ipswich. The same glacial features re-occurred several times and with changes in the levels of the North Sea the great Stour successively changed its course, depth and width. Alluvial deposits that included not only fine river deposits good for farming, as seen close to the railway line but also gravels and sand were laid along the river bed. The gravels are even now being dredged up at Collingdale and elsewhere in the parish the deposits of sand often appear in road cuttings.

 

Visitors to England coming by way of Dover will be met with the magnificent white walls of England – the massy chalk cliffs where the northern rim of the downs has been cut athwart by the rush of waters that severed the islands from mainland Europe. These selfsame chalk rocks, as mentioned before, form the escarpment that rises above Wye. The cretaceous chalk is distinguished by three layers – the oldest being the Lower Chalk , the second oldest being the Middle Chalk and the youngest the Upper Chalk. These chalks are fairly easy to discriminate and there are good sample areas to be found in the local area.

  • The Upper Chalk – is white, brittle almost pure calcium carbonate, hard chalk is believed to develop slowly. It contains many, large flint (chalcedony) nodules. Some flint nodules are hollow and display quartz crystals, others the remnants of fossilized sponges. The Upper Chalk above the Crown is concealed by Plateau Drift in which occasional echinoids derived from the Upper Chalk may be found.
  • The Middle Chalk – most of the Wye escarpment is made up of Middle Chalk. It is about 60 metres thick here. It is mostly hard and brittle. Some 30 m or more has been exposed in the quarry below the Crown. Fossils are relatively rare – mostly echinoids and Inoceramus fragments. The lower 6 m of the Middle Chalk is composed of a relatively hard and nodular form of chalk called Melbourne Rock.
  • The Lower Chalk

 

The bottom of the chalk escarpment has been known as Holmsdale for centuries and is reputedly, from archaeological records, to be one of the first places in Kent to be settled. Holmsdale stands on the Gault Clay and this selfsame clay can be found outcropping at East Wear Bay to the east of Copt Point, Folkestone. This location has been the site of many a fossil find but in our own area it is also possible to find fossils of the Gault Clay. The most spectacular location is the old clay pit at Naccolt where the Gault used to dug for the Ashford Brick Company. There ammonites, belemnites and fish vertebrae can be found mainly on the surrounding surface where the clay has been washed away. The pit is now filled with water and is within a private land owned by Southern Water (?). Like many fossil sites this is dangerous even with permission.

 

While the Gault clay is heavy and difficult to work its very impervious nature facilitates its action as a barrier to the water that percolates down through the chalk of the Downs. Consequently where the Gault/Chalk interface is close to the surface springs will break through (see Map **). One such spring is supposed to have healing properties – Saint Eustace’s Spring close by Withersdane. On the Parish Map of 1747 there are several such springs marked in Bridge Street. Although they were culverted a few years ago damage to the culvert resulted in the spring near Wye Primary School breaking out and causing considerable subsidence in the road. Likewise beyond the Oxenturn Road surgery a spring that seems to be repeatedly ignored causes road flooding especially if the ditch is left to deteriorate. Ditches were formally dug across the foot of the scarp to drain away the considerable spring water runoff. Many of these ditches have fallen into serious disrepair or neglect. It would be wise at this time of warnings of more severe weather if farmers were to ensure that these ditches are regularly maintained. At the same time the surface soils of the land between the North Downs and the river tend to be rich and fertile though of use for different kinds of farming.