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Museum Expeditions & Field Trips - 1999


ABBEY WOOD & CHARLTON - MARCH 1999

ABBEY WOOD
Abbey Wood SSSI

In conjunction with the Open University Geological Society, a field trip was undertaken to Lesnes Abbey Wood, in south east London. Lesnes Abbey itself is now but a ruin set in landscaped gardens, but the site backs onto a densely wooded hill that commands excellent views across London. High on the hill, hidden within the woods, is a small patch of open sand rich in sharks teeth, bivalve shells and fish vertebrae and otoliths dating from the Eocene (55 million years ago). The small Visitor Centre to the west of the abbey ruins has a display of the better fossil finds from the site, that includes a slab of shell breccia that forms the base of the deposit some 8 metres below ground level.

Abbey Wood is also a designated 'SSSI' - Site of Special Scientific Interest - because of the tiny Tertiary mammal teeth that have been found there. Despite being a registered SSSI, Abbey Wood is open to local fossil hunters, with prior consent of the Bexley Ranger Service, on the understanding that no excavations are made below 18" (about 45cm). This is to preserve the beds that contain the mammal teeth. Anyone fortunate to find one during a dig (difficult to impossible as these teeth are almost microscopic) is requested to contact the Natural History Museum in London.

The Blackheath Sand itself is lightly coloured, soft and similar to that found on the most popular beach resorts. It is possible to see fossils of all types lying on the surface, but the best lie hidden and need to be sieved out. Like any sand deposit, the top 5-10cm when dry is easily sieved dry. Below this level, where the sand is damp and clumps together, it is necessary to sieve with water. Given that the nearest water supply is a garden tap at the Ranger Station next to the Abbey Visitor Centre, some 15 minutes walk away, it is advisable to take jerry-cans to limit the number of trips needed.

A sieve with a 3-4mm mesh is about right to capture most of the more common fossils found here. A larger mesh will let through too many, a smaller one makes sieving out the sand hard work. Imagine therefore the amount of effort that is needed to find the mammal teeth for which the site is famous as these need a sieve size of 0.5mm!

Fossils found included:-

Shark TeethBivalves

Other fossils collected included the Gastropods - Melanopsis antediluviana and Tympanotones funatus. A fish vertebra, a number of other bivalve shell fragments and partial gastropods, were also found.

CHARLTON
Gilbert's Pit

This trip took us to what was a large sand quarry 'Gilbert's Pit' now disused since the 1960s. The interior of the quarry is accessible from road level and is now a grassed over playing field. The slopes of the quarry face, and the ridge that rises above the north face, are now tree lined and overgrown. The main face of the quarry faces south and is reached through a wicket gate set into the steel containment fence. This gate is locked for safety reasons but access can be arranged via the local authority.

As with all quarry access, extreme care must be taken with the wearing of stout boots and hard hats highly recommended.

The main face of the quarry is much eroded through landslip and the scree slope is rich in whole brachiapod and bivalve fossils, both loose and still with some attached matrix. This site is also of Eocene age but unlike Abbey Wood, contains no shark teeth. Instead, some 8 feet below the crest of the ridge an exposure of Lewisham Leaf Beds may be found but the fossil leaves are usually heavily pyritised and poorly preserved.

The deposits here are from the Blackheath Beds with abundant Blackheath Pebbles embedded in the surrounding sandy matrix.

Bivalves

A number of the Blackheath pebbles were also collected the largest of which weighed in at an extraordinary 1.35kg.


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BLUEWATER, DARTFORD, KENT - SEPTEMBER 1999
Bluewater

This site, formerly one of the largest chalk pits in the North Kent area has been turned into a massive out-of-town regional shopping centre. The centre is built on the quarry floor and surrounded on all four sides by the old quarry faces. The designers of the centre have landscaped the surrounding area with paths, gardens and lakes.

While most of the faces and scree slopes have been fenced off and cannot be accessed, it is still possible (with care because of the road system built around Bluewater) to get to much of the north face of the quarry. However, this is not a site to collect fossils. Most of these have long gone along with the chalk mined here for decades and apart from the occasional fragment of the bivalve Inoceramus, ubiquitous to the upper chalk, pickings are extremely slim.

This is a site to walk around and look at, visible features including in-fill solution pipes, flint banding and, unusually, a clear fault line visible in the north face by the emergency vehicle access road next to the coach park.


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