Natural wonders of London

THERE ARE FOSSIL TREES IN REGENT'S PARK

Look on the shores of the lake in Queen Mary's Garden and you will see two areas of short stubby tree trunks.

Trees from millions of years ago can be found in Regent's Park

These are relics of an ancient forest that grew about 140 million years ago!

However, they did not grow in London - they have been brought from Dorset and placed in Regent's Park by the Royal Botanic Society in 1840.

The trunk belongs to a kind of conifer tree that grew well in the very hot and arid conditions of Britain during the Jurassic period.

The wood became preserved in silica (quartz) when the trees were suddenly inundated by a very salty (hypersaline) sea.

They were literally pickled where they stood.

LONDON HAS ITS OWN NATURAL FRESH WATER SUPPLY

London has a natural source of fresh water trapped in the Chalk beneath the city.

The water is trapped because chalk is very permeable and water falling on the North Downs or in the Chilterns runs into the basin.

It is kept within this layer because the chalk is sandwiched between two clays: the Gault Clay beneath and the London Clay above.

As London's population and industry grew this water supply was not enough and other sources were found from the rivers.

However, with less industry now using this water supply there is a fast-rising water table and buildings in London are now becoming at risk of flooding.

THE THAMES DID NOT ALWAYS FLOW THROUGH LONDON

The Thames is a very young feature of London's landscape.

The River Thames only flowed through London 500,000 years ago

It only came this way for the first time half a million years ago (a very short time in geological terms).

Before this time it flowed from the Midlands through Oxfordshire, turning north eastwards through Hertfordshire and East Anglia.

It entered the North Sea at Ipswich.

The change in the river's course came when a huge ice sheet came across England (from Scandinavia) and blocked the old river valley.

When the ice started to melt and huge amounts of water entered this old Thames river system in Oxfordshire it dramatically cut down a new route through the Chalk - the Goring Gap - to emerge a new river flowing down through Bucks, Berks and into London.

That certainly changed the way London was to develop from that day onwards.

NEANDERTHALS ROAMED LONDON

Skull fragments have been found within the Thames river terraces at Swanscombe - known affectionately as the 'Swanscombe Man', but is now believed to be a woman!

These bones are about 250,000 years old and the bones and tools indicate that she was a Neanderthal and would have been in a small group living a hunter-gather life-style.

GEOLOGY HELPS THE UNDERGROUND STAY UP

Much of the underground train network is tunnelled into the London Clay.

Much of the tube network goes through London clay

Clays are soft and easy to dig into, but this clay holds its shape surprisingly well and so will not collapse or sludge back again!

However, other geology sometimes causes problems - there are sands in the rock sequence that contain pyrite (otherwise known as 'fools gold').

When water with oxygen passes through these the result is a very acid water which attacks and corrodes metal pipes of underground structures - oops.

WHY IS HAMPSTEAD A HEATH?

Hampstead is a heath as the hill has a thick capping of sands known as the Bagshot Sands.

This allows good drainage and an acid soil to develop.

Interestingly, the water quickly seeps through the sands to reach the impermeable London clay halfway down the hill - the result is the line of springs.

Article courtesy of Dr Jill Eyers Open University Associate Lecturer, freelance geologist and geoarchaeologist.