Brickearth

Last updated
Brickearth deposits exposed as the topmost orange red layer in the cliff at Milford on Sea, Hampshire, UK Milford on Sea, Rook Cliff - geograph.org.uk - 1744521.jpg
Brickearth deposits exposed as the topmost orange red layer in the cliff at Milford on Sea, Hampshire, UK

Brickearth is a term originally used to describe superficial windblown deposits found in southern England. The term has been employed in English-speaking regions to describe similar deposits.

Brickearths are periglacial loess, a wind-blown dust deposited under extremely cold, dry, peri- or postglacial conditions. The name arises from its early use in making house bricks, its composition being suitable for brick-making without additional material being added and unlike clay its bricks can be hardened (fused) at lower temperatures, including in wood-fired kilns.

The brickearth is normally represented on 1:50,000 solid and drift edition geological maps. [1] In the Thames valley, in broad patches brickearth overlies fluvial terrace gravel; it has been reclassified on later maps as the "Langley Silt Complex". [2]

Description

Brickearth is a superficial deposit of homogeneous loam or silt [3] deposited during the Pleistocene geological period. [4] Brickearth typically occurs in discontinuous spreads, across southern England and South Wales, south of a line from Pembroke in the west to Essex in the east in depths of up to a metre. Commercially useful deposits of about 2m to 4m thick are present in Kent, Hertfordshire and Hampshire, overlying chalk, Thanet Beds or London Clay. The original deposition of the sediments occurred under cold climates where fluvial out-wash sediments from glaciers were subject to windy dry periods. The exposed finer-grained sediments were picked up and transported by the wind and were deposited wherever the wind strength decreased. [5]

There are extensive brickearth deposits in Kent, particularly on the North Downs dip slope and on the Hoo peninsula, sections of the Medway and Stour valleys. Its mineral content is critical to its applicability in brickmaking and requires precise proportions of chalk, clay, and iron. [6] Brickearth requires little or no admixture of other materials to render it suitable for the manufacture of 'stock bricks'. [3] In 1986, four active stock brick works were in Kent: at Otterham Quay, Funton, Murston and Ospringe.

The brickearth gives rise to rich and fertile soils which have been exploited for agriculture. [7] It is prone to rapid 'collapse' settlement when saturated with water and does not provide a firm foundation for buildings. [6]

In Chichester, the brickearth is a flint-rich brown silty clay up to five metres thick, which occurs on the coastal plain. The brickearth is unfossiliferous but occasionally yields man-made flint implements. [4]

When used for brick making, it was often dug from small temporary holes and baked into bricks on the spot in brick clamps, and used for building nearby. The hole often remained and became a pond.

Related Research Articles

<span class="mw-page-title-main">Loess</span> Sediment of accumulated wind-blown dust

A loess is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loesses or similar deposits.

<span class="mw-page-title-main">North Downs</span> Range of hills in south east England, UK

The North Downs are a ridge of chalk hills in south east England that stretch from Farnham in Surrey to the White Cliffs of Dover in Kent. Much of the North Downs comprises two Areas of Outstanding Natural Beauty (AONBs): the Surrey Hills and the Kent Downs. The North Downs Way National Trail runs along the North Downs from Farnham to Dover.

<span class="mw-page-title-main">Geology of Hertfordshire</span>

The geology of Hertfordshire describes the rocks of the English county of Hertfordshire which are a northern part of the great shallow syncline known as the London Basin. The beds dip in a south-easterly direction towards the syncline's lowest point roughly under the River Thames. The most important formations are the Cretaceous chalks, which are exposed as the high ground in the north and west of the county, and the Cenozoic rocks made up of the Paleocene age Reading beds and Eocene age London Clay that occupies the remaining southern part.

<span class="mw-page-title-main">Geology of Dorset</span>

Dorset is a county in South West England on the English Channel coast. Covering an area of 2,653 square kilometres (1,024 sq mi); it borders Devon to the west, Somerset to the north-west, Wiltshire to the north-east, and Hampshire to the east. The great variation in its landscape owes much to the underlying geology, which includes an almost unbroken sequence of rocks from 200 to 40 million years ago (Mya) and superficial deposits from 2 Mya to the present. In general, the oldest rocks appear in the far west of the county, with the most recent (Eocene) in the far east. Jurassic rocks also underlie the Blackmore Vale and comprise much of the coastal cliff in the west and south of the county; although younger Cretaceous rocks crown some of the highpoints in the west, they are mainly to be found in the centre and east of the county.

<span class="mw-page-title-main">Drift (geology)</span> Material of glacial origin

In geology, drift is a name for all sediment transported by a glacier and deposited directly by or from the ice, or by glacial meltwater. Drift is often subdivided into unstratified drift that forms moraines and stratified drift that accumulates as stratified and sorted sediments in the form of outwash plains, eskers, kames, varves, and so forth. The term drift clay is a synonym for boulder clay. Both are archaic terms for glacial tills with a fine-grained matrix.

<span class="mw-page-title-main">Lambeth Group</span>

The Lambeth Group is a stratigraphic group, a set of geological rock strata in the London and Hampshire Basins of southern England. It comprises a complex of vertically and laterally varying gravels, sands, silts and clays deposited between 56-55 million years before present during the Ypresian age. It is found throughout the London Basin with a thickness between 10m and 30m, and the Hampshire Basin with a thickness between 50m and less than 25m. Although this sequence only crops out in these basins, the fact that it underlies 25% of London at a depth of less than 30m means the formation is of engineering interest for tunnelling and foundations.

The Ancestral Thames is the geologically ancient precursor to the present day River Thames. The river has its origins in the emergence of Britain from a Cretaceous sea over 60 million years ago. Parts of the river's course were profoundly modified by the Anglian glaciation some 450,000 years ago. The extensive terrace deposits laid down by the Ancestral Thames over the past two million years or so have provided a rich source of material for studies in geology, geomorphology, palaeontology and archaeology.

Superficial deposits refer to geological deposits typically of Quaternary age for the Earth. These geologically recent unconsolidated sediments may include stream channel and floodplain deposits, beach sands, talus gravels and glacial drift and moraine. All pre-Quaternary deposits are referred to as bedrock.

<span class="mw-page-title-main">Geology of London</span>

The geology of London comprises various differing layers of sedimentary rock upon which London, England is built.

<span class="mw-page-title-main">Geology of Kansas</span>

The geology of Kansas encompasses the geologic history and the presently exposed rock and soil. Rock that crops out in the US state of Kansas was formed during the Phanerozoic eon, which consists of three geologic eras: the Paleozoic, Mesozoic and Cenozoic. Paleozoic rocks at the surface in Kansas are primarily from the Mississippian, Pennsylvanian, and Permian periods.

<span class="mw-page-title-main">Norwich Crag Formation</span>

The Norwich Crag Formation is a stratigraphic unit of the British Pleistocene Epoch. It is the second youngest unit of the Crag Group, a sequence of four geological formations spanning the Pliocene to Lower Pleistocene transition in East Anglia. It was deposited between approximately 2.4 and 1.8 million years ago, during the Gelasian Stage.

The geology of Suffolk in eastern England largely consists of a rolling chalk plain overlain in the east by Neogene clays, sands and gravels and isolated areas of Palaeocene sands. A variety of superficial deposits originating in the last couple of million years overlie this 'solid geology'.

The geology of Essex in southeast England largely consists of Cenozoic marine sediments from the Palaeogene and Neogene periods overlain by a suite of superficial deposits of Quaternary age.

The geology of Kent in southeast England largely consists of a succession of northward dipping late Mesozoic and Cenozoic sedimentary rocks overlain by a suite of unconsolidated deposits of more recent origin.

The geology of Norfolk in eastern England largely consists of late Mesozoic and Cenozoic sedimentary rocks of marine origin covered by an extensive spread of unconsolidated recent deposits.

The geology of West Sussex in southeast England comprises a succession of sedimentary rocks of Cretaceous age overlain in the south by sediments of Palaeogene age. The sequence of strata from both periods consists of a variety of sandstones, mudstones, siltstones and limestones. These sediments were deposited within the Hampshire and Weald basins. Erosion subsequent to large scale but gentle folding associated with the Alpine Orogeny has resulted in the present outcrop pattern across the county, dominated by the north facing chalk scarp of the South Downs. The bedrock is overlain by a suite of Quaternary deposits of varied origin. Parts of both the bedrock and these superficial deposits have been worked for a variety of minerals for use in construction, industry and agriculture.

<span class="mw-page-title-main">Geology of Surrey</span>

The geology of Surrey is dominated by sedimentary strata from the Cretaceous, overlaid by clay and superficial deposits from the Cenozoic.

This article describes the geology of the Broads, an area of East Anglia in eastern England characterised by rivers, marshes and shallow lakes (‘broads’). The Broads is designated as a protected landscape with ‘status equivalent to a national park’.

The geology of the South Downs National Park in South East England comprises a gently folded succession of sedimentary rocks from the Cretaceous and early Palaeogene periods overlain in places by a range of superficial deposits from the last 2.6 million years. Whereas the South Downs are formed from the Late Cretaceous age chalk, the South Downs National Park extends into the Weald to the north of the range and thereby includes older rock strata dating from the Early Cretaceous including sandstones and mudstones. The youngest solid rocks are found on the southern fringes of the National Park in the eastern extension of the Hampshire Basin and include sand, silt and clay deposited during the Palaeocene and Eocene epochs.

References

  1. BGS solid and drift edition 1:50,000 Maps
  2. Gibbard, P. L., 1985 Pleistocene History of the Middle Thames Valley
  3. 1 2 Kent Minerals Subject Plan, BrickEarth Written Statement, May 1986, Kent County Council Planning Department. Accessed April 2012
  4. 1 2 Pleistocene Archived October 16, 2007, at the Wayback Machine Chichester Museum website. Accessed April 2012
  5. Geodiversity Character Area Descriptions GCA 1 Tendring Plateau Archived 2016-03-04 at the Wayback Machine Geo-East Partnership Accessed April 2012
  6. 1 2 Loessic Brickearth Map at Physical Properties and Behaviour of UK Rocks and Soils. British Geological Survey, National Environmental Research Council. Accessed April 2012
  7. Tendring Essex Geodiversity poster Archived May 7, 2013, at the Wayback Machine Peter Allen, Gerald Lucy, Teresa O’Connor, David Bridgland, William George, Adrian Gascoyne, Adrian Knowles, Tom White. Quaternary Research Association, Geo Essex . Accessed April 2012

doi: 10.1144/GSL.QJEGH.1996.029.P2.04 May 1996 Quarterly Journal of Engineering Geology and Hydrogeology, 29, 147-161.