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Horsenden Hill
Horsenden Hill (/ˈhɔːrsəndən/; grid reference TQ 161 843) is a hill and open space, located between the Perivale, Sudbury, and Greenford areas of West London. It is in the London Borough of Ealing, close to the boundary with the London Borough of Brent. It is one of the higher eminences in the local area, rising to 85 m (276 ft) above sea level, and the summit forms part of the site of an ancient hillfort. It is the site of a trig point, TP4024.
The base of this isolated hill is at an altitude of approximately 50 metres. Like all of the immediately surrounding area, the base of the hill, as well as the slopes of the hill up to about 70m, are on London Clay. Between about 70m and 80m is an isolated layer of sandier Claygate Beds. Both deposits are of Eocene age, dated at about 50 million years ago.
At the top of the hill, from about 80m to the summit at 85m, is a small and relatively thin layer of much younger Dollis Hill Gravel. This permeable gravel has to some extent protected the easily-eroded London Clay below from being removed. It is not uncommon to find hills in the London area which are capped by a protective layer of sand or gravel, with London Clay below. Another example is Barn Hill (Wembley), to the north-east. Barn Hill also has a cap of Dollis Hill Gravel. So too does Dollis Hill itself. Like Horsenden Hill, both are isolated hills rising above lower ground on London Clay.
The Dollis Hill Gravel was deposited more than half a million years ago by a river which flowed from well to the south and continued to the north-east, through the "Finchley depression" towards Hoddesdon in Hertfordshire. This is known because about 7% of the gravel, which is otherwise composed mostly of flint, consists of a hard stone called chert, which can only come from Lower Greensand beds found to the south in Surrey. The river was probably an ancestor of the River Wey in Surrey.
This gravel was probably a much more extensive deposit in this part of the London area than it is now.
The river which deposited the Dollis Hill Gravel at Horsenden Hill eventually flowed into the River Thames around Hoddesdon. At that time, the Thames was itself flowing on a course different from today's, roughly on a line through Burnham Beeches, the Vale of St Albans, Harlow, Chelmsford and Colchester.
Approximately 450,000 years ago, during the Anglian Stage, ice from northern Britain reached as far south as north London. A lobe of this ice advanced up the valley whose river had previously deposited the Dollis Hill Gravel.
As the ice moved up the valley (it eventually reached at least as far as Finchley), the water being brought from the south by the "proto-Wey" river was blocked. So a huge lake developed in front of the advancing ice sheet. Lacustrine deposits left by this lake have been identified in Finchley and Hendon.
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Horsenden Hill
Horsenden Hill (/ˈhɔːrsəndən/; grid reference TQ 161 843) is a hill and open space, located between the Perivale, Sudbury, and Greenford areas of West London. It is in the London Borough of Ealing, close to the boundary with the London Borough of Brent. It is one of the higher eminences in the local area, rising to 85 m (276 ft) above sea level, and the summit forms part of the site of an ancient hillfort. It is the site of a trig point, TP4024.
The base of this isolated hill is at an altitude of approximately 50 metres. Like all of the immediately surrounding area, the base of the hill, as well as the slopes of the hill up to about 70m, are on London Clay. Between about 70m and 80m is an isolated layer of sandier Claygate Beds. Both deposits are of Eocene age, dated at about 50 million years ago.
At the top of the hill, from about 80m to the summit at 85m, is a small and relatively thin layer of much younger Dollis Hill Gravel. This permeable gravel has to some extent protected the easily-eroded London Clay below from being removed. It is not uncommon to find hills in the London area which are capped by a protective layer of sand or gravel, with London Clay below. Another example is Barn Hill (Wembley), to the north-east. Barn Hill also has a cap of Dollis Hill Gravel. So too does Dollis Hill itself. Like Horsenden Hill, both are isolated hills rising above lower ground on London Clay.
The Dollis Hill Gravel was deposited more than half a million years ago by a river which flowed from well to the south and continued to the north-east, through the "Finchley depression" towards Hoddesdon in Hertfordshire. This is known because about 7% of the gravel, which is otherwise composed mostly of flint, consists of a hard stone called chert, which can only come from Lower Greensand beds found to the south in Surrey. The river was probably an ancestor of the River Wey in Surrey.
This gravel was probably a much more extensive deposit in this part of the London area than it is now.
The river which deposited the Dollis Hill Gravel at Horsenden Hill eventually flowed into the River Thames around Hoddesdon. At that time, the Thames was itself flowing on a course different from today's, roughly on a line through Burnham Beeches, the Vale of St Albans, Harlow, Chelmsford and Colchester.
Approximately 450,000 years ago, during the Anglian Stage, ice from northern Britain reached as far south as north London. A lobe of this ice advanced up the valley whose river had previously deposited the Dollis Hill Gravel.
As the ice moved up the valley (it eventually reached at least as far as Finchley), the water being brought from the south by the "proto-Wey" river was blocked. So a huge lake developed in front of the advancing ice sheet. Lacustrine deposits left by this lake have been identified in Finchley and Hendon.