77-647: The River Brent is a river in west and northwest London, England, and a tributary of the River Thames . 17.9 miles (28.8 km) in length, it rises in the Borough of Barnet and flows in a generally south-west direction before joining the Tideway stretch of the Thames at Brentford . A letter from the Bishop of London in 705 suggesting a meeting at Breġuntford , now Brentford , is
154-427: A certain amount of glaciofluvial material deposited by meltwater flowing from the front of the ice lobe). That stream, which would quickly have cut back to the ice front at Henly's Corner, would have been the incipient River Brent. Dollis Brook and Mutton Brook would have there flowed into this new stream. And the new stream would have been joined on its right bank by former tributaries of the proto-Mole-Wey river, notably
231-567: A diverted course from Uxbridge to Richmond, from where it continued, in a broadly eastwards direction, towards the North Sea. This caused the lake in the proto-Mole-Wey valley to be drained, thus leaving the former islands in the lake as isolated hills in what is now the London Clay basin of the north-western section of the River Brent catchment area. As illustrated on a geological map of the area, it
308-421: A fire starter. The exact mode of formation of flint is not yet clear, but it is thought that it occurs as a result of chemical changes in compressed sedimentary rock formations during the process of diagenesis . One hypothesis is that a gelatinous material fills cavities in the sediment, such as holes bored by crustaceans or molluscs and that this becomes silicified . This hypothesis would certainly explain
385-400: A new river, to be given its own name, perhaps one already known to the people who live upon its banks. Conversely, explorers approaching a new land from the sea encounter its rivers at their mouths, where they name them on their charts, then, following a river upstream, encounter each tributary as a forking of the stream to the right and to the left, which then appear on their charts as such; or
462-533: A trigger, strikes a hinged piece of steel (" frizzen ") at an angle, creating a shower of sparks and exposing a charge of priming powder. The sparks ignite the priming powder and that flame, in turn, ignites the main charge, propelling the ball, bullet, or shot through the barrel. While the military use of the flintlock declined after the adoption of the percussion cap from the 1840s onward, flintlock rifles and shotguns remain in use amongst recreational shooters. Flint and steel used to strike sparks were superseded in
539-508: Is also referred to in places as the "proto-Mole-Wey".) These deposits are found at what is today the so-called Finchley Gap , and to the north-east and south-west of it. Dollis Hill Gravel is found, for example, south-west of the Gap at Hendon and Horsenden Hill , and north-east of the Gap over wide areas from Southgate to Goff's Oak . Today, the highest of those deposits rest at an altitude of around 100 metres (for example at Muswell Hill ). So
616-412: Is commonly included in survival kits . Ferrocerium is used in many cigarette lighters, where it is referred to as "a flint". Flint's utility as a fire starter is hampered by its property of uneven expansion under heating, causing it to fracture, sometimes violently, during heating. This tendency is enhanced by the impurities found in most samples of flint that may expand to a greater or lesser degree than
693-563: Is one of the primary materials used to define the Stone Age . During the Stone Age, access to flint was so important for survival that people would travel or trade long distances to obtain the stone. Grime's Graves was an important source of flint traded across Europe. Flint Ridge in Ohio was another important source of flint, and Native Americans extracted the flint from hundreds of quarries along
770-480: Is referred to above. But then the River Thames established its newly-diverted course. That course appears to have run along a line approximately from Uxbridge to Northolt Park, Perivale, Richmond and Streatham Hill. The newly-diverted Thames thus cut across the floor of the proto-Mole-Wey valley. And being a very powerful river, it would also have cut down below the level of that valley floor to some extent. Water from
847-417: Is striking that Dollis Brook, for the greater part of its length between Barnet Playing Fields and Henly's Corner, follows a north-south line close to the western limit of glacial till left by the ice sheet lobe which extended to Finchley. Similarly, Mutton Brook follows an east-west line which is close to the southern limit of glacial till left by the ice sheet lobe. This is because, as the ice sheet lobe in
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#1732844913569924-486: Is today a dissected plateau which lies to the south-east of the Vale of St Albans. This plateau stretches from Bushey Heath to Northaw and beyond, and is capped over wide areas, at altitudes ranging from about 150 metres to 130 metres, by a fairly thin (average 3 metres) layer of sand and gravel known as Pebble Gravel (or, in places, Stanmore Gravel). Although flint is the main component of this gravel, it has been known since
1001-563: Is today the Brent catchment area would have been very different from today's topography, because the Pebble Gravel was laid down on a valley floor, whereas today it occupies the highest ground in the area. The relief has thus been inverted. But, in 1979, P.L. Gibbard mapped younger deposits, known as Dollis Hill Gravel and named after one of the locations where this deposit is found, which were also laid down by an ancestral Mole-Wey river. (This river
1078-753: The Jurassic deposits of the Kraków area and Krzemionki in Poland, as well as of the Lägern ( silex ) in the Jura Mountains of Switzerland. In 1938, a project of the Ohio Historical Society , under the leadership of H. Holmes Ellis began to study the knapping methods and techniques of Native Americans . Like past studies, this work involved experimenting with actual knapping techniques by creation of stone tools through
1155-446: The mineral quartz , categorized as the variety of chert that occurs in chalk or marly limestone . Historically, flint was widely used to make stone tools and start fires . Flint occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones . Inside the nodule, flint is usually dark grey or black, green, white, or brown in colour, and has a glassy or waxy appearance. A thin, oxidised layer on
1232-436: The 20th century by ferrocerium (sometimes referred to as "flint", although not true flint, " mischmetal ", "hot spark", "metal match", or "fire steel"). This human-made material, when scraped with any hard, sharp edge, produces sparks that are much hotter than obtained with natural flint and steel, allowing use of a wider range of tinders. Because it can produce sparks when wet and can start fires when used correctly, ferrocerium
1309-543: The 400,000 years which followed the Anglian stage, rivers and streams incised themselves more deeply into the underlying strata. That erosion mostly took place in periods of "high discharge, under cold climatic conditions" when river flow was augmented and when vegetation was thin. In particular, the River Thames, which, in the vicinity of Hanger Lane was at a today's altitude of around 70 metres when it first established its diverted course, had probably cut down to about 60 metres by
1386-542: The Anglian glaciation, in the area currently covered by the Brent catchment area, are not known with any certainty. But it is known that, elsewhere, some tributaries of rivers which were themselves severely disrupted by that glaciation today still follow broadly the same lines as their pre-glaciation valleys. This is the case, for example, for certain tributaries of the upper River Lea, such as the Rivers Mimram and Stort. So it seems reasonable to suggest that parts at least of
1463-425: The Anglian glaciation. After reaching as far south as Ware, about 450,000 years ago, lobes of this ice sheet extended up two valleys, oriented south-west to north-east - that of the proto-Thames (which, by this time was flowing along the line of the Vale of St Albans, and where an ice lobe extended to Watford), and that of the proto-Mole-Wey (where the other lobe extended to Finchley). In the early twentieth century it
1540-508: The Brent catchment area, as in much of the London Basin , is Eocene London Clay . This is mostly a stiff blue-brown clay, over 100 metres thick. In some higher parts of the area, a relatively thin, upper part of the London Clay formation, sandier in content and known as the Claygate Beds , is also found. In some areas of relatively limited extent, such as on the higher parts of Harrow on
1617-460: The Brent is much younger in age. An Ancestral Thames is thought to have come into being over 60 million years ago, during the post- Cretaceous uplift of Britain (an uplift which was tilted to the south-east). The Brent, as a southward-flowing, left-bank tributary of the Thames, was formed as a result of the Anglian glaciation, which occurred about 450,000 years ago. In the early twentieth century, it
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#17328449135691694-572: The Carpenders Park gap (today followed by the West Coast Main (railway) Line between London Euston and Watford), the Thames overspill surged through Wealdstone and Kenton. The land it crossed would have been bare of vegetation and very susceptible to fluvial erosion. The powerful overflow quickly eroded areas of higher ground. This could have included a possible ridge of higher ground running from Stanmore to Colindale (separating ancestral valleys of
1771-469: The Dollis Hill Gravel thus flowed along a line broadly similar to that of today's River Brent, but in the opposite direction, from south-west to north-east. The gradient of the floor of that valley in the area now occupied by the Brent catchment was low - probably no more than 50 cm per kilometre. The number, and courses, of the tributary streams which flowed into the proto-Mole-Wey river prior to
1848-493: The Finchley pro-glacial lake would thus have flowed down into the Thames and would have been carried away by it. As mentioned earlier, the lake would thus have dried up. A stream would then have cut back from the Thames, probably from around Hanger Lane. That stream probably cut back in a north-easterly direction along the line of the former proto-Mole-Wey valley bottom (the near-flat surface of which would by then have been covered by
1925-507: The Hill , Hampstead and Highgate , the London Clay and Claygate Beds are overlain by sandy Eocene Bagshot Beds . All these formations are overlain in several areas by much younger, Pleistocene formations, principally fluvial deposits and glacial deposits. The oldest Pleistocene deposit, Pebble Gravel, is found across the upper, northern margin of the catchment area, from Bushey Heath to Chipping Barnet. The most recent Pleistocene deposits include
2002-458: The River Thames. It was clear from the broad course which Wooldridge plotted for this river that it was an ancestor of the River Mole (and/or River Wey ). In 1994, D.R. Bridgland proposed that Pebble Gravel (or Stanmore Gravel) which is located on Harrow Weald Common (near Bushey Heath) was deposited by an ancestral Mole-Wey, and that that river was a tributary of the River Thames at a time when
2079-484: The Wealdstone Brook and Silk Stream), similar to and parallel with the ridge that still exists and that runs from Barnet Gate to Mill Hill. The overflow thus carved out much of the London Clay basin which today forms the north-western section of the River Brent catchment area. In particular, it probably removed much of the Dollis Hill Gravel which must have been situated in this area prior to the Anglian glaciation. At
2156-525: The Wealdstone Brook and the Silk Stream. As the ice sheet melted, that incipient River Brent would have been heavily loaded with glaciofluvial material flowing from the melting ice, and from the till which the ice sheet was leaving behind. It appears that, at Hanger Lane, near its initial confluence with the Thames, the Brent was forced to deposit a large quantity of that material. In doing so it may also have been forced to move to its current course, slightly to
2233-858: The best toolmaking flint has come from Belgium (Obourg, flint mines of Spiennes ), the coastal chalks of the English Channel , the Paris Basin , Thy in Jutland (flint mine at Hov), the Sennonian deposits of Rügen , Grimes Graves in England, the Upper Cretaceous chalk formation of Dobruja and the lower Danube (Balkan flint), the Cenomanian chalky marl formation of the Moldavian Plateau (Miorcani flint) and
2310-418: The brook at barely 60 metres, in a distance of only about one kilometre. A sizable section of that slope would have been the result of fluvial incision since the Anglian stage. During its post-Anglian incision, the Thames in this area moved in a southward direction. As it did so, it laid down river terrace deposits (mostly sand and gravel) of decreasing age and altitude. The Thames-Brent confluence also moved to
2387-515: The chalky-soil country of France, the British filled sandbags with flint and used these sandbags as breastworks. Flint pebbles are used as the media in ball mills to grind glazes and other raw materials for the ceramics industry. The pebbles are hand-selected based on colour; those having a tint of red, indicating high iron content, are discarded. The remaining blue-grey stones have a low content of chromophoric oxides and so are less deleterious to
River Brent - Misplaced Pages Continue
2464-424: The coasts of South-East England or Western France, were calcined to around 1,000 °C (1,800 °F). This heating process both removed organic impurities and induced certain physical reactions, including converting some of the quartz to cristobalite . After calcination the flint pebbles were crushed and milled to a fine particle size. However, the use of flint has now been superseded by quartz . Because of
2541-452: The colour of the ceramic composition after firing. Until recently calcined flint was also an important raw material in clay-based ceramic bodies produced in the UK. In clay bodies , calcined flint attenuates the shrinkage whilst drying, and modifies the fired thermal expansion. Flint can also be used in glazes as a network former. In preparation for use flint pebbles, frequently sourced from
2618-570: The complex shapes of flint nodules that are found. The source of dissolved silica in the porous media could be the spicules of silicious sponges ( demosponges ). Certain types of flint, such as that from the south coast of England and its counterpart on the French side of the Channel , contain trapped fossilised marine flora. Pieces of coral and vegetation have been found preserved inside the flint similar to insects and plant parts within amber . Thin slices of
2695-438: The confluence of the Brent with the Thames at Brentford. Broadly speaking, the catchment area can be divided into three topographical zones: - a southern zone, lying south of a line from about Harlesden to Northolt, which is of low relief and which (apart from the hill at Hanger Lane) lies below an altitude of 40 metres; - a basin-like north-western zone which is surrounded by areas of higher ground which rise fairly steeply to
2772-540: The earliest record of this place and probably therefore that of the river, suggesting that the name may be related to the Celtic * brigant- meaning "high" or "elevated", perhaps linked to the goddess Brigantia . (For the purposes of this section, the Brent catchment area is taken to include the catchment areas of all its tributaries.) The catchment area varies in altitude from just over 150 metres above sea level at Bushey Heath, on its northern watershed, to barely 10 metres at
2849-406: The end of the Anglian stage, and is now at an altitude of barely 10 metres at Kew. In thus cutting down by about 50 metres since the Anglian stage, the Thames would thus have lowered the base level of rivers and streams in the Brent catchment area, and they too have cut down to a notable degree in places, even though they obviously had much less erosive power than the much-larger Thames. For example,
2926-439: The first-order tributary being typically the least in size. For example, a second-order tributary would be the result of two or more first-order tributaries combining to form the second-order tributary. Another method is to list tributaries from mouth to source, in the form of a tree structure , stored as a tree data structure . Flint Flint , occasionally flintstone , is a sedimentary cryptocrystalline form of
3003-414: The flint, in a similar (but more time-consuming) way. These methods remain popular in woodcraft, bushcraft, and amongst people practising traditional fire-starting skills. A later, major use of flint and steel was in the flintlock mechanism , used primarily in flintlock firearms, but also used on dedicated fire-starting tools. A piece of flint held in the jaws of a spring-loaded hammer, when released by
3080-451: The handedness is from the point of view of an observer facing upstream. For instance, Steer Creek has a left tributary which is called Right Fork Steer Creek. These naming conventions are reflective of the circumstances of a particular river's identification and charting: people living along the banks of a river, with a name known to them, may then float down the river in exploration, and each tributary joining it as they pass by appears as
3157-428: The ice retreated, the two streams continued along the same courses that they had been forced to follow by the ice lobe - between glacial till and the higher ground of Mill Hill, etc in the case of Dollis Brook, and between glacial till and Hampstead Heath, etc in the case of Mutton Brook. At the time of the ice lobe, those two streams would at first have flowed into the pro-glacial lake in the proto-Mole-Wey valley which
River Brent - Misplaced Pages Continue
3234-424: The joining of tributaries. The opposite to a tributary is a distributary , a river or stream that branches off from and flows away from the main stream. Distributaries are most often found in river deltas . Right tributary , or right-bank tributary , and left tributary , or left-bank tributary , describe the orientation of the tributary relative to the flow of the main stem river. These terms are defined from
3311-471: The junction of Dollis Brook and Mutton Brook today is at an altitude of just under 50 metres. When the proto-Mole-Wey river was flowing through this locality prior to the Anglian glaciation, it was at an altitude of 68 metres. And Dollis Brook is relatively steep-sided in certain sections - for example, around Woodside Park, where the ground falls from over 90 metres altitude on the Finchley High Road to
3388-445: The large stronghold of Framlingham Castle . Many different decorative effects have been achieved by using different types of knapping or arrangement and combinations with stone ( flushwork ), especially in the 15th and early 16th centuries. Because knapping flints to a relatively flush surface and size is a highly skilled process with a high level of wastage, flint finishes typically indicate high status buildings. During World War I, in
3465-490: The late nineteenth century that it also contains in places a notable quantity of chert derived from Lower Greensand Beds in the Weald. It was suggested early on that this "pointed to the former existence of streams from that area". S.W. Wooldridge later suggested that it was in fact "a river of major dimensions" (which) "entered from the south" that was responsible for transporting much of this chert to areas which are now north of
3542-408: The latter river was flowing to the north-west of the Vale of St Albans. That could have been nearly two million years ago. He also suggested that similar gravel, located further north-east near Northaw at a slightly lower altitude, was also deposited by an ancestral Mole-Wey, but at a later date (which could have been around 1.75 million years ago). At those times, the topography of the country in what
3619-474: The material more homogeneous and thus more knappable and produces tools with a cleaner, sharper cutting edge. Heat treating was known to Stone Age artisans. When struck against steel, a flint edge produces sparks. The hard flint edge shaves off a particle of the steel that exposes iron, which reacts with oxygen from the atmosphere and can ignite the proper tinder . Prior to the wide availability of steel, rocks of pyrite (FeS 2 ) would be used along with
3696-503: The network of tributary streams which flowed into the proto-Mole-Wey river, in the area currently covered by the Brent catchment area, proved to be equally robust. Thus, it is possible that, although the proto-Mole-Wey river itself was completely replaced by the River Brent during the Anglian glaciation, and parts of those of its tributaries which came into contact with the ice front were diverted (as described below), other sections of today's network of Brent tributaries broadly reflect parts of
3773-556: The next section), at a today's altitude of about 90 metres, and joined a precursor of the Pymmes Brook in the vicinity of East Barnet. That precursor brook may then have flowed south-eastwards to join the proto-Mole-Wey somewhere around New Southgate. It has been known since the nineteenth century that an ice sheet once descended from the north of England as far as north London and left behind extensive spreads of till and other glacial deposits. This ice advance has since been identified as
3850-427: The north, with its junction with the Thames thus moving to the west, in the vicinity of Greenford. Thus, by end of the Anglian stage, the current drainage network in the Brent catchment area had broadly been established. But the rivers and streams in the network at that time would then have been flowing at a higher level, relative to their altitudes today. On average, this could have been around 20–30 metres higher. In
3927-462: The opposite bank before approaching the confluence. An early tributary is a tributary that joins the main stem river closer to its source than its mouth, that is, before the river's midpoint ; a late tributary joins the main stem further downstream, closer to its mouth than to its source, that is, after the midpoint. In the United States, where tributaries sometimes have the same name as
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#17328449135694004-482: The outside of the nodules is usually different in colour, typically white and rough in texture. The nodules can often be found along streams and beaches . Flint breaks and chips into sharp-edged pieces, making it useful in constructing a variety of cutting tools, such as knife blades and scrapers. The use of flint to make stone tools dates back more than three million years; flint's extreme durability has made it possible to accurately date its use over this time. Flint
4081-476: The perspective of looking downstream, that is, facing the direction the water current of the main stem is going. In a navigational context, if one were floating on a raft or other vessel in the main stream, this would be the side the tributary enters from as one floats past; alternately, if one were floating down the tributary, the main stream meets it on the opposite bank of the tributary. This information may be used to avoid turbulent water by moving towards
4158-511: The post-Anglian river terrace deposits of the Thames and Brent rivers in Ealing and other southern parts of the catchment area. Glacial till is found in the north-eastern sector of the catchment area, around Finchley. Current topography is largely the result of landform evolution during the Pleistocene epoch (that is, during the last two million years or so). Although a tributary of the River Thames,
4235-604: The pre-Anglian network of tributary streams which fed the proto-Mole-Wey. This could apply to, for example, the upper part of the Dollis Brook, the Folly Brook, the Silk Stream and the Wealdstone Brook. In the case of the uppermost section of the Dollis Brook, which runs broadly west-east from Barnet Gate towards Barnet Playing Fields, it is possible that, immediately prior to the Anglian glaciation, that stream continued eastwards (where it now turns southwards, for reasons explained in
4312-409: The proto-Mole-Wey valley around Finchley, in the sense of being an area of lower ground lying between higher ground on either side (for example, at Mill Hill and Hampstead Heath, both at altitudes of over 120 metres today), must have existed by the time those highest deposits of Dollis Hill Gravel were laid down. That could have been around one million years ago. The proto-Mole-Wey river which laid down
4389-424: The proto-Thames valley towards Watford, the passage of the river was blocked, and its water backed up to form a lake in front of the advancing ice. That lake eventually extended as far up the proto-Thames valley as a point south of Gerrards Cross, where lacustrine deposits have been identified. The water in that lake eventually rose to relatively low points on the interfluve with the proto-Mole-Wey catchment area to
4466-624: The ridge. This "Ohio Flint" was traded across the eastern United States, and has been found as far west as the Rocky Mountains and south around the Gulf of Mexico . When struck against steel, flint will produce enough sparks to ignite a fire with the correct tinder , or gunpowder used in weapons , namely the flintlock firing mechanism . Although it has been superseded in these uses by different processes (the percussion cap ), or materials ( ferrocerium ), "flint" has lent its name as generic term for
4543-643: The river into which they feed, they are called forks . These are typically designated by compass direction. For example, the American River in California receives flow from its North, Middle, and South forks. The Chicago River 's North Branch has the East, West, and Middle Fork; the South Branch has its South Fork, and used to have a West Fork as well (now filled in). Forks are sometimes designated as right or left. Here,
4620-410: The same time, a lake formed in front of the ice lobe which was moving south-westwards up the proto-Mole-Wey valley towards Finchley, and which was blocking the flow of the proto-Mole-Wey river. The swirling waters of that lake also caused considerable erosion of the previous topography. But isolated islands, mostly capped by Dollis Hill Gravel, were left within the lake. The Thames eventually established
4697-418: The smaller stream designated the little fork, the larger either retaining its name unmodified, or receives the designation big . Tributaries are sometimes listed starting with those nearest to the source of the river and ending with those nearest to the mouth of the river . The Strahler stream order examines the arrangement of tributaries in a hierarchy of first, second, third and higher orders, with
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#17328449135694774-524: The south, with the River Brent thus extending its course by over five kilometres, from Greenford to Hanwell, then to Brentford. As the Brent moved southwards, it cut down through the river terrace deposits which had been laid down by the Thames. During the post-Anglian period, the River Brent itself left river terrace deposits in places. An older one is a Boyn Hill deposit just north of Brent Reservoir at an altitude of 60 metres. Younger ones include almost continual stretches of Taplow and Kempton Park deposits in
4851-415: The south-east, where that water could overflow into that catchment area. Two such points were at Carpenders Park and Uxbridge. Water overflowed into the proto-Mole-Wey catchment in a considerable volume and with considerable force (to the extent that, in the case of the overflow at Uxbridge, the Thames in due course established a completely new course through that route). In the case of the overflow through
4928-523: The stone often reveal this effect. Flint sometimes occurs in large flint fields in Jurassic or Cretaceous beds, for example, in Europe. Puzzling giant flint formations known as paramoudra and flint circles are found around Europe but especially in Norfolk, England, on the beaches at Beeston Bump and West Runton . The "Ohio flint" is the official gemstone of Ohio state. It is formed from limey debris that
5005-432: The streams are seen to diverge by the cardinal direction (north, south, east, or west) in which they proceed upstream, sometimes a third stream entering between two others is designated the middle fork; or the streams are distinguished by the relative height of one to the other, as one stream descending over a cataract into another becomes the upper fork, and the one it descends into, the lower ; or by relative volume:
5082-545: The surrounding stone, and is similar to the tendency of glass to shatter when exposed to heat, and can become a drawback when flint is used as a building material . Flint, knapped or unknapped, has been used from antiquity (for example at the Late Roman fort of Burgh Castle in Norfolk) up to the present day as a material for building stone walls, using lime mortar, and often combined with other available stone or brick rubble. It
5159-487: The use of techniques like direct freehand percussion, freehand pressure and pressure using a rest. Other scholars who have conducted similar experiments and studies include William Henry Holmes , Alonzo W. Pond , Francis H. S. Knowles and Don Crabtree . To reduce susceptibility to fragmentation, flint/chert may be heat-treated, being slowly brought up to a temperature of 150 to 260 °C (300 to 500 °F) for 24 hours, then slowly cooled to room temperature. This makes
5236-443: The valley bottom and adjacent slopes downstream of Brent Reservoir. Tributary A tributary , or an affluent , is a stream or river that flows into a larger stream ( main stem or "parent" ), river, or a lake . A tributary does not flow directly into a sea or ocean . Tributaries, and the main stem river into which they flow, drain the surrounding drainage basin of its surface water and groundwater , leading
5313-448: The valley of the proto-Mole-Wey river moved up that valley, it would have blocked streams flowing down towards that river from higher ground to the west and south. In particular, it would have forced the eastward-flowing Dollis Brook to have turned to the south, alongside the western edge of the ice lobe (and likewise for Folly Brook). And it would have forced northward-flowing drainage coming down from Highgate and Hampstead to have turned to
5390-463: The water out into an ocean. The Irtysh is a chief tributary of the Ob river and is also the longest tributary river in the world with a length of 4,248 km (2,640 mi). The Madeira River is the largest tributary river by volume in the world with an average discharge of 31,200 m /s (1.1 million cu ft/s). A confluence , where two or more bodies of water meet, usually refers to
5467-531: The west (Harrow on the Hill), north (Bushy Heath) and east (Mill Hill), and where several isolated hills such as Horsenden Hill, Barn Hill and Dollis Hill are located; and - a north-eastern zone consisting of the relatively narrow and steep-sided valleys of the Dollis Brook, Folly Brook and Mutton Brook; and of the high ground which surrounds those valleys (at Hampstead Heath, Whetstone, Totteridge, Chipping Barnet, etc). The oldest and most extensive geological formation in
5544-512: The west, alongside the southern edge of the ice lobe (thus forming Mutton Brook). Fed by meltwater from the adjacent ice sheet, these streams would have cut down quickly along their new routes. And later, when the ice sheet retreated, a substantial thickness of till was left behind where the ice once sat. (For example, in the locality of the Finchley Gap, the ice left glacial deposits which today are up to 18 metres in thickness.) Consequently, after
5621-426: Was concluded that the Thames must have been diverted to its more southerly course of today by the ice advance up the Vale of St Albans to Watford. As noted above, the proto-Mole-Wey river was a tributary of the proto-Thames. It flowed northwards from the Weald, then passed through what is today the Brent catchment area (but in the opposite direction to the flow of today's River Brent). As an ice sheet lobe advanced up
5698-440: Was deposited at the bottom of inland Paleozoic seas hundreds of millions of years ago that hardened into limestone and later became infused with silica . The flint from Flint Ridge is found in many hues like red, green, pink, blue, white, and grey, with the colour variations caused by minute impurities of iron compounds. Flint can be coloured: sandy brown, medium to dark grey, black, reddish brown or an off-white grey. Flint
5775-423: Was most common in those parts of southern England where no good building stone was available locally, and where brick-making was not widespread until the later Middle Ages. It is especially associated with East Anglia , but also used in chalky areas stretching through Hampshire , Sussex, Surrey and Kent to Somerset . Flint was used in the construction of many churches, houses, and other buildings, for example,
5852-565: Was suggested that the River Thames, after descending through Oxfordshire , entering the London Basin near the Goring Gap and running north-east from there, continued in that direction prior to the ice advance, past Watford and along the line of the Vale of St Albans. This hypothesis has since been confirmed by much subsequent research. That "proto-Thames" river received tributaries from the south. At least one of those tributaries traversed what
5929-546: Was used in the manufacture of tools during the Stone Age as it splits into thin, sharp splinters called flakes or blades (depending on the shape) when struck by another hard object (such as a hammerstone made of another material). This process is referred to as knapping . Flint mining is attested since the Paleolithic , but became more common since the Neolithic (Michelsberg culture, Funnelbeaker culture ). In Europe, some of
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