GLA 20: Horsenden Hill

GLA 20: Horsenden Hill, Proposed RIGS
London Borough of Ealing, TQ 16256 84381
Ownership: Local Authority. Public open space.

Horsenden Hill is one of the highest points in North West London with excellent views of the surrounding area. At 85 m it is not as high as Harrow-on-the-Hill to the north (120 m) but the steeple of St. Mary’s can quite clearly be seen. There is a view over the valley between the two hills.

The Geology

This site is a hill in the London Clay capped by the Claygate Beds (both of Eocene age, dated at about 50 million years) with the much younger Dollis Hill Gravel Formation lying over them at the top of the hill. The London Clay underlies most of London as the name implies but only on the isolated hills nearer to the centre is it overlain by the Claygate Beds which are sandier than the underlying clay, implying that they were laid down nearer the shore.

The Dollis Hill Gravel is a river deposit from a tributary of the pre-diversionary Thames. It now forms hill-caps that decline in elevation northwards, indicating deposition in a south-bank tributary of the ancestral Thames. The exact date is uncertain but is likely to be around 2 million years old. The gravel is composed of angular flint (58%), rounded flint (32%), quartz/quartzite (1.8%) and Lower Greensand chert (7%) (see BGS Special Memoir, p. 55-57). The latter indicates that the tributary originated in the Weald to the south of London at a time before the Thames was diverted by the Anglian glaciation that reached as far south as north London 450,000 years ago. It did not quite reach Horsenden Hill. Only after that time was the ‘London Valley’ as we know it created.

Exposures of all three rock types are hard to find. The Dollis Hill Gravel is better exposed at Barn Hill in Fryent Country Park to the northeast where there are also views to Harrow-on-the-Hill. At 86m Barn Hill is much the same height as Horsenden Hill but the Claygate Beds are reportedly absent.

Access

Public access via the road that runs along the west side of the hill, Horsenden Hill North. There is a car park near the top of the hill on the north side with free parking. The top of the hill can be reached by a steep, maintained path from the car park. The Capital Ring runs through the site (http://www.wlklondon.org.uk).

gla20View of area with information board
Source: London’s foundations, page 154

 

 

 

 

Site Map OS Topography © Crown Copyright
Source: London’s foundations, page 153

gla20 map

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