Clay-with-Flints
Encyclopedia
In geology
, Clay-with-Flints was the name given by W. Whitaker in 1861 to a peculiar deposit of stiff red, brown or yellow clay
containing unworn whole flint
s as well as angular shattered fragments, also with a variable admixture of rounded flint, quartz
, quartzite
and other pebbles. It occurs in sheets or patches of various sizes over a large area in the south of England
, from Hertfordshire
on the north to Sussex
on the south, and from Kent
on the east to Devon
on the west. It almost always lies on the surface of the Upper Chalk, but in Dorset
it passes on to the Middle and Lower Chalk, and in Devon it is found on the Chert-Beds of the Selbornian group (A. J. Jukes-Browne, The Clay-with-Flints, its Origin and Distribution, Q.J.G.S., vol. lxii., 1906, p. 132).
Many geologists have supposed, and some still hold, that the Clay-with-Flints is the residue left by the slow solution and disintegration of the Chalk by the processes of weathering; on the other hand, it has long been known that the deposit very frequently contains materials foreign to the Chalk, derived either from the Tertiary rocks or from overlying drift. There is evidence against the view that the deposit is mainly a Chalk residue, This shows that many patches of the Clay-with-Flints lie upon the same plane and may be directly associated with Reading Beds. He concludes that the material of the Clay-with-Flints has been chiefly and almost entirely derived from Eocene
clay, with addition of some flints from the Chalk; that its presence is an indication of the previous existence of Lower Eocene Beds on the same site and nearly, at the same relative level, and, consequently, that comparatively little Chalk has been removed from beneath it. Finally, I think that the tracts of Clay-with-Flints have been much more extensive than they are now. Clay-with-flint is a nutrient rich substance unlike chalk.(bc. cit. p. 159).
It is noteworthy that the Clay-with-Flints is developed over an area which is just beyond the limits of the ice sheets of the Glacial
epoch, and the peculiar conditions of late Pliocene and Pleistocene times; involving heavy rain
, snow
and frost, may have had much to do with the mingling of the Tertiary and Chalky material. Besides the occurrence in surface patches, Clay-with-Flints is very commonly to be observed descending in pipes often to a considerable depth into the Chalk; here, if anywhere, the residual chalk portion of the deposit should be found, and it is surmised that a thin layer of very dark clay with darkly stained flints, which appears in contact with the sides and bottom of the pipe, may represent all there is of insoluble residue.
A somewhat similar deposit, a congbomirat de silex or argile a silex, occurs at the base of the Eocene on the southern and western borders of the Paris
basin, in the neighborhood of Chartres, Thimerais and Sancerrois.
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, Clay-with-Flints was the name given by W. Whitaker in 1861 to a peculiar deposit of stiff red, brown or yellow clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
containing unworn whole flint
Flint
Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. Inside the nodule, flint is usually dark grey, black, green, white, or brown in colour, and...
s as well as angular shattered fragments, also with a variable admixture of rounded flint, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, quartzite
Quartzite
Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...
and other pebbles. It occurs in sheets or patches of various sizes over a large area in the south of England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
, from Hertfordshire
Hertfordshire
Hertfordshire is a ceremonial and non-metropolitan county in the East region of England. The county town is Hertford.The county is one of the Home Counties and lies inland, bordered by Greater London , Buckinghamshire , Bedfordshire , Cambridgeshire and...
on the north to Sussex
Sussex
Sussex , from the Old English Sūþsēaxe , is an historic county in South East England corresponding roughly in area to the ancient Kingdom of Sussex. It is bounded on the north by Surrey, east by Kent, south by the English Channel, and west by Hampshire, and is divided for local government into West...
on the south, and from Kent
Kent
Kent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...
on the east to Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
on the west. It almost always lies on the surface of the Upper Chalk, but in Dorset
Dorset
Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...
it passes on to the Middle and Lower Chalk, and in Devon it is found on the Chert-Beds of the Selbornian group (A. J. Jukes-Browne, The Clay-with-Flints, its Origin and Distribution, Q.J.G.S., vol. lxii., 1906, p. 132).
Many geologists have supposed, and some still hold, that the Clay-with-Flints is the residue left by the slow solution and disintegration of the Chalk by the processes of weathering; on the other hand, it has long been known that the deposit very frequently contains materials foreign to the Chalk, derived either from the Tertiary rocks or from overlying drift. There is evidence against the view that the deposit is mainly a Chalk residue, This shows that many patches of the Clay-with-Flints lie upon the same plane and may be directly associated with Reading Beds. He concludes that the material of the Clay-with-Flints has been chiefly and almost entirely derived from Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
clay, with addition of some flints from the Chalk; that its presence is an indication of the previous existence of Lower Eocene Beds on the same site and nearly, at the same relative level, and, consequently, that comparatively little Chalk has been removed from beneath it. Finally, I think that the tracts of Clay-with-Flints have been much more extensive than they are now. Clay-with-flint is a nutrient rich substance unlike chalk.(bc. cit. p. 159).
It is noteworthy that the Clay-with-Flints is developed over an area which is just beyond the limits of the ice sheets of the Glacial
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
epoch, and the peculiar conditions of late Pliocene and Pleistocene times; involving heavy rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
, snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
and frost, may have had much to do with the mingling of the Tertiary and Chalky material. Besides the occurrence in surface patches, Clay-with-Flints is very commonly to be observed descending in pipes often to a considerable depth into the Chalk; here, if anywhere, the residual chalk portion of the deposit should be found, and it is surmised that a thin layer of very dark clay with darkly stained flints, which appears in contact with the sides and bottom of the pipe, may represent all there is of insoluble residue.
A somewhat similar deposit, a congbomirat de silex or argile a silex, occurs at the base of the Eocene on the southern and western borders of the Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
basin, in the neighborhood of Chartres, Thimerais and Sancerrois.