The Streets of Southwark

 

The Streets of Southwark

 

The Landscape of Southwark, its Geology and Prehistory

 

Southwark is part of an extensive area of marsh and flood plain on the south side of the River Thames, a flood plain extending from Lambeth in the west to Rotherhithe and Greenwich in the east, eventually going all the way to Dartford, Gravesend and the Thames Estuary. This ground is part of the broad Thames Valley and is mostly made up of silt and alluvial deposits of sand and gravel laid down by the Thames over a period of about 400,000 years, all overlying a thick and much older layer of London Clay.

 

The geological history of an area like Southwark may seem remote and detached from our everyday experience of the streets we know and live in today, but its importance is fundamental to an understanding of how and why such a place came to exist. The topograpgy is like a matrix in which our civilization grew, it is the starting point for everything we see on the ground today. Below our feet, as we stand in a place like Borough High Street, are layers of gravel, clay, chalk, and sandstone, all of which were laid down over many millions of years. Alternating periods of sea and dry land swept across most of what we now call south east England, and these periods laid down many distinct layers of sedimental rock types, such as clay, chalk and sandstone.

 

These layers are generally not visible in London, but they can easily be seen in the Weald in Kent where the land has been eroded away to reveal them, particularly at the North and South Downs.

 

The earlier layers, created during the Lower Cretaceous Period, are formed of alternating clay and sandstone, the most recent being called Lower Greensand, Gault Clay and Upper Greensand. Above them is a thick layer of chalk, formed from the shells and skeletons of sea creatures that lived during the Upper Cretaceous Period, a time when the sea became warm and deep and tropical and free of muddy river silts and sediments.

 

During the Eocene epoch, between 56 and 33 million years ago, the sea encroached over the whole of the London area and laid down a heavy layer of sediment known as London Clay, which underlies the whole of central London and its suburbs.

 

This basic and easily understood layering was subjected to larger geologic forces, particularly the movement of vast tectonic plates of continental size that pressed against each other and forced the layers of rock into the complex folds that we see as mountains, hills and valleys.

 

For the history of Southwark, and for Britain as a whole, the most important tectonic plate movement happened between 65 and 55 million years ago, when the continent of Africa pushed against the continent of Europe. By sheer pressure this collision caused the creation of the Alps. Solid rock was forced up to 4,810 meters above sea level, as at Mont Blanc, the highest mountain in the alps. The pressure was so great that land as far north as the British Isles was squeezed and distorted. The Weald in Kent was formed by forcing the land upwards, creating a huge dome called an anticline, which is defined today by the line of the North and South Downs. The inverse happened in central London, where the fold was downwards, called a syncline, creating a broad, shallow valley extending from the North Downs in Kent south-east of London to the Chiltern Hills north-west of London. This valley became known as the London or Thames Valley. Southwark lies right at the bottom of this valley.

 

To make things more complicated, the last few million years saw the Ice Age descend on us. The Ice Age was a sequence of alternating cold and warm periods, called glacial and interglacial periods. These alternating periods moulded the surface of the land by using thick, deep layers of ice and slow moving glaciars to scour the land, cutting U shaped valleys in places like the Scottish Glens and the present Lake District of England.

 

The Thames has always been one of the most important drainage systems for the southern area of England, capturing water from as far west as the Welsh hills, the Cotswolds and the Chilterns and leading it east towards the North Sea. Its course, however, was not fixed and it moved as geological and climatic forces intervened. It appears to have originally flowed west to east to the north of London, through the Vale of St Albans and on through Essex till it reached the North Sea at Clacton, or reached the Rhine which at times lowed up the area now covered by the North Sea. This course to the north of London could have been permanent, but climate change intervened and diverted the river south through the place where London was to be born.

 

It was some 400,000 years ago that the Thames first came to flow through the London valley. This was during the Ice Age. The Ice Age was a long sequence of cold periods, called glaciations, when the ice advanced south from the pole, and warmer interglaciations, when the ice retreated and the climate was milder. The most severe glaciation was called the Anglian Stage, which happened between about 478,000 and 424,000 years ago. Conditions were so cold that the ice sheet advanced to just north of London, blocking off the Vale of St Albans. Suddenly there was no escape route for the water of the Thames and its tributaries. A lake built up to the south and west of St Albans along the valley of the River Colne, and eventually this lake overflowed at Staines-on-Thames, from which point the river carved a new route eastwards towards the sea, a route through the place we now know as London.

 

Once in London, the Thames meanded and created a series of sand and gravel terraces rising upwards as we move back from each side of the river . The first terrace is known as the Kempton Park Terrace, or simply as Kempton Park Gravel. Southwark lies partly on Thames silt and mud and partly on a section of this very low gravel terrace, which in our area extends from Lambeth in the west to Rotherhithe in the east. Moving south from the Thames embankment, the terrace begins at a line marked roughly by The Cut and Union Street and extends south to Walworth. Everything to the north of this gravel terrace is built on Thames mud and silt.

 

In addition, there are a number firm gravel outcrops closer to the Thames, as at Thorny Isle at Westminster, at the Strand close by Covent Garden, at Cannon Street, at London Bridge, at Tower Hill and at Wapping. At Southwark, the outcrops were clustered around the Borough and Bermondsey area, where they formed islands or eyots in a broad expanse of mud flats. At low tide they were joined to the land, but at high tide they were isolated and surrounded by water channels. These eyots became focal points, places where there was firm ground close to the edge of the river, places where people could find crossing points, perhaps by finding a natural ford, as at Westminster, or perhaps by building a bridge, as at Vauxhall and at London Bridge.

 

At the Borough and in Bermondsey there were several significant eyots, significant because they were the places where building could begin.

 

The most important of these eyots, and the ones where building could start, were in The Borough around Southwark Cathedral and at the foot of London Bridge, at Horsleydown just south of Tower Bridge, and at Bermondsey.

 

We know from archaeological discoveries made throughout the area that it was occupied by prehistoric and Iron Age peoples from the Ice Ages to the coming of the Romans in AD 43. The landscape familiar to these early inhabitants would have looked much like Erith, Crayford and Dartford Marshes look today, as seen in the photograph of Crayford Marshes below. (Illus. 1.)

 

 

Crayford Marshes

 

Illus. 1. This photograph of Crayford Marshes is (apart from the line of suburban houses in the background) very much the way St. George's Fields would have looked when the Romans arrived in AD 43. It was flat marshland with ponds, ditches and tussocks of grass, perhaps with the occasional tree.