Head describes
deposits
A deposit account is a bank account maintained by a financial institution in which a customer can deposit and withdraw money. Deposit accounts can be savings accounts, current accounts or any of several other types of accounts explained below.
...
consisting of fragmented material which, following
weathering
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement) ...
, have moved downslope through a process of
solifluction
Solifluction is a collective name for gradual processes in which a mass moves down a slope ("mass wasting") related to freeze-thaw activity. This is the standard modern meaning of solifluction, which differs from the original meaning given to it ...
. The term has been used by British geologists since the middle of the 19th century to describe such material in a range of different settings from flat hilltops to the bottoms of valleys. Areas identified as head include deposits of
aeolian origin such as
blown sand and
loess, slope deposits such as
gelifluctates and
solifluctates, and recently eroded
soil
Soil, also commonly referred to as earth or dirt
Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty.
Common types of dirt include:
* Debri ...
material, called
colluvium
Colluvium (also colluvial material or colluvial soil) is a general name for loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rainwash, sheetwash, slow continuous downslope creep, or a variable combinati ...
. With geologists becoming more interested in studying the near-surface environment and its related processes, the term head is becoming obsolete.
A related term is 'combe (or coombe) rock', descriptive of a body of
chalk
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...
and
flint
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and sta ...
fragments contained within a mass of chalky earth typically found on the
chalk downland
Downland, chalkland, chalk downs or just downs are areas of open chalk hills, such as the North Downs. This term is used to describe the characteristic landscape in southern England where chalk is exposed at the surface. The name "downs" is deriv ...
s of south-east England and resulting from freeze-thaw processes. Where the mass is also soliflucted, it is considered a variety of head.
Though its earliest use is attributed to De la Beche in 1839 he mentions that in 1837 Mr. Trevelyn of Guernsey observed “ a bed of disintegrated granite, about three feet thick, mixed with angular fragments, thus reminding us of the head of angular fragments so commonly seen in Cornwall and Devon.“
[ Proceedings of the Geol. Society of London, Vol.ii. p.577 ( Nov.15, 1837)]
References
Deposition (geology)
Geochronology
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