I guess the word ‘geology’ will leave most people running scared but this is what my degree was in so I actually get quite excited by it, that aside the geology of Highbrooms, the very ground beneath our feet, has had a massive influence on the development of Highbrooms and it must be included as a precursor to looking at the industrial history of this area from the last century in a bit more detail.
The rocks beneath Highbrooms and the surrounding area were formed during the early Cretaceous period, beginning about 136 million years ago. The oldest beds are the Ashdown sands, and as the name suggests they are mainly formed from sands and silts that were deposited into the freshwater Wealden lake by many rivers.
These sands are followed by the Wadhurst clays which accumulated in the extensive Wealden lake. These clays are iron-rich, with the iron often formed as nodules. The abundance of easily accessible iron led to the early iron-working industry during Roman times and then to a far greater extent in medieval times when there was a greater demand for then iron to produce armaments, such as the cast-iron canon, for supply to the continuous European wars. The heavily forested Weald also supplied the charcoal for smelting and had fast flowing streams that powered the furnaces.
The Tunbridge Wells sands formed above the Wadhurst clays, and these can be seen today in the area around Tunbridge Wells forming the outcrops typical of the high Weald, having been shaped during the last ice age. The youngest deposits in the area consist of the heavy Weald clay.
The Ashdown Beds, Wadhurst Clay and Tunbridge Wells Sandstones are grouped together to form the ‘Hastings Beds’, which reaches a maximum thickness of about 400m in the Weald. It comprises of three major cycles of sedimentation in which claystones and mudstones coarsen upwards into cross-bedded sandstones (a fine example is visible in the ‘cave’ at the Mount Edgcumbe in Tunbridge Wells) with a capping of frequently bone-rich gravel.
The climate during the formation of the Wealden beds was warm. Fossil plant remains indicate that the swamp and its bordering lands supported vegetation that consisted of primitive plants, namely gymnosperms, ferns and the horsetail, Equisetites. The horsetails are an indication that the water depths over the Weald were very shallow, as are the occurrence of dessication cracks.
The indigenous fauna of the Wealden swaps consist almost exclusively of lamellibranchs, gastropods and ostracods, there are also rare occurrences of fish and marine reptiles.
As mentioned in a previous entry one the most noticeable finds in the Wadhurst clay was the bones of an Iguanodon in the Highbrooms brickworks pits during 1933. These bones, along with moulds of footprints, can be found in the Tunbridge Wells museum natural history room.
After deposition of the Wealden Series, subsidence extended across a wider area of south east England, the sea broke into the swamp and the beds were overlain by marine sands and clays, and eventually the chalk was deposited from the calcite skeletons of coccoliths that lived in the warm shallow seas at the end of the Cretaceous period, 65 million years ago.
During the Tertiary period the subsidence in the Wealden basin ceased and was replaced with uplift which continues today.
Tectonic events to the south, principally the Alpine Orogeny (also responsible for the uplift and formation of the Alps!), during the mid-tertiary period caused the anticlinal folding seen in the Weald today. The softer chalk beds, still seen forming the prominent ridges of the North and South downs, and underlying Gault clay and Lower Greensands were eroded away from the centre of the Weald revealing the beds of sand and clay below.
I hope that this has been an interesting blog and not too scientific as is meant to be an introduction to the local geology, not too in-depth or boring! Sorry if I failed….
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