Marlow Common Clay Pits Marlow Common is one of 200 commons in the Chilterns which have been shaped by centuries of local history. As you walk in this lovely part of Buckinghamshire today it is difficult to imagine a time when it was not grass and woodland. However, the rocks beneath your feet tell an amazing story of Marlow Common over the past 80 million years. It is a story that takes us from flooding by a shallow chalky sea to a tropical landscape with waterlogged clay soils, and finally to the frozen wastes of the Ice Age. It was these extremes in climate that laid down the geological layers, but it was local people who finally shaped it into what we see today. The geological story 1. Marlow under a tropical climate Chalk The Chalk is pure limestone made from tiny skeletons of algae. They settled out in a tropical sea during a massive global warming. Climate started to warm dramatically at around 95 million years ago. This event was to continue for the next 30 million years, finally ending 65 million years ago. During this time the world became much hotter – resulting in a global average temperature of about 30 degrees (compared to 15 degrees today). As climate warmed, ice melted, and sea level rose. As the world warmed further the water in the oceans expanded and the result was a very large proportion of all land on Earth being flooded by shallow seas. This of course included the whole of what is now England, including Marlow Common. These seas were teeming with life and some of these animals are preserved as fossils within the chalk and inside flint nodules – both have been found nearby and on the common. A sea urchin preserved in flint A sponge preserved in Chalk, one of the most common fossils 1 Clay-with-flint After 30 million years of global warming, the Earth gradually returned to more normal temperatures from 65 million years ago. This resulted in sea level falling which exposed the whole of England as land again, including Buckinghamshire, which was exposed as a flat ancient sea bed. Rain dissolved huge quantities of chalk resulting in a residual layer on top composed of clay and flints – as neither of these dissolve in rainwater. Clay-with-flints – the result of 20 million years of dissolved Chalk. Reading Formation clays From 60 to 50 million years ago the Chalk seas had retreated and Bucks was a hot, tropical landscape. The flat landscape produced waterlogged soils resulting in the quality clays later used for the local brick and pottery industry. The Reading Formation clays are not shown in the geological section as they are no longer present in sufficient quantity to map. They were excavated during the 19th to earliest 20th century. However, the first geological map to be produced was later in the 20th century and so they were never seen on Marlow Common by geologists. Nonetheless, hints of where they were, how they were excavated and how much clay was there, can be seen in clues remaining in the landscape today. We know very little about the geological history in Marlow after 50 million years ago, as erosion has removed much of the evidence. However, we know from elsewhere that Buckinghamshire remained very flat during most of this time, until the start of the Ice Age 2.6 million years ago. It was during the Ice Age that the Chiltern Hills were formed and the mighty Thames was born and cut down into the valley we know today. 2 The rock sequence at Marlow Common. Oldest rocks at the bottom, youngest on the top. A section through the rock layers from the Hambleden Valley to the Thames in Marlow, showing the landscape and the different layers under each area. The Ice Age deposits are like icing on the main ‘rock cake’. 3 The geological story 2. Marlow as tundra on the edge of the ice Sands and gravels of the River Thames Gravels are obvious in some parts of the Common – their presence indicated by acid-loving plants such as heather, gorse and oak. The rounded pebbles found in the footpaths show they are from a river. The pebbles are mostly flint, but whitish quartz pebbles may be found along with duller, very round, pale brown sandstone. These pebbles are part of the Gerrards Cross Gravels and record a time when the ancient River Thames flowed here before cutting down to its present level in Marlow. The Thames cut down and left a gravel terrace during each big freeze when ice advanced towards and sometimes over England. This down-cutting is preserved in ten stages for the whole Thames valley and three of these events are visible from Marlow Common and down the hill towards Marlow. The geological section shows Winter Hill and then Taplow, and finally Shepperton Gravels each successively at lower levels - and each successively younger. The youngest sediment of all is the modern-day alluvium in the river. Rivers cut down incrementally this way as a result of sea level falling when water is locked up in ice sheets. Sea level is the ‘base’ level to which all rivers flow, and if it lowers, so the river entry point is lowered. This has a knock-on effect upstream. The result is the old level left high in the slope or cliff face as a terrace with the old sands and gravels high and dry. Thames gravels showing the direction of water flow as inclined lines. Dry valleys While major dry valleys were being cut to the west (as the Hambleden Valley) and to the east (the Wye valley) Marlow Common was within a smaller catchment area draining down to the newly forming Thames river. The steeper slopes of Lords Wood were cut by melting snow and ice flowing over frozen ground (tundra). Dry valleys only form during cold phases when the ground is frozen – in other words, in a tundra environment. Each time the Chilterns became tundra the pores of the Chalk were blocked with ice and so when the ice and snow started to melt, the result is water forced to flow over the frozen ground. This cuts a ‘V’ shaped river valley which is so distinctive of water flow, but the dry valleys today look flatter as much sediment and debris has collected at the bottom. 4 Brick and tile industry on Marlow Common Evidence for this past industry comes in the form of numerous pits and sinuous depressions as well as house names such as Kiln Cottage and the Old Kiln House. The clay used was from the Reading Formation, and the products were mostly bricks and tiles. There was also a quality terracotta ware produced, which may be seen at Monks Corner as a long frieze panel. This was called Medmenham Ware and was produced by the sculptor Conrad Dressler between 1898 to 1905. Dressler was born in London in 1856 and became the design manager of the works. The pottery and kiln was owned by Robert Hudson, who made his fortune as a soap magnate. He bought Medmenham Abbey, arranged for its restoration and then went on to design and build a number of estate houses such as Westfield Cottages, Medmenham. The pottery was built in order to support and encourage rural crafts – as Hudson was an admirer of the Arts and Crafts ideas of William Morris. The company advertised the fact that they were proud to use local materials and employ village work people. The products were high quality, handmade or moulded forms and bespoke to order. Their advertising lists the types and the top quality raised tile was priced at an average of 30 shillings per yard. Architects soon made use of this quality product for prestigious buildings such as the Sunlight Chambers in Dublin and the Law Society Hall in London. Tiles are on display in the V&A Museum in London. Local examples may be found for instance as a frieze panel at Jerome Cottage (Monks Corner). The name of the house is notable as the home of Jerome K. Jerome, author of Three men in a boat c. 1910 to 1920. Medmenham Ware frieze panel at Monks Corner. The 1898 map of the common shows the old clay pits along with the two brick kilns in operation at that time. The common would have been an unpleasant place to live at that time. The area would be taken up with extraction pits and piles of clay exposed for weathering. There would be ‘puddling’ areas for processing the clay, vast drying areas for moulded bricks, and during the firing days, the air would be thick with smoke. 5 In addition to the main extraction pits there were a number of smaller pits. These were never mapped as they were short-lived and very small. A walk around the common today will reveal many undulations, rounded depressions and sinuous trenches where small pockets were ‘chased’ by small work teams for this valuable clay. A deep sinuous excavation removing pockets of brick-making clay. Looking at the total area of pits from map and modern evidence it can be calculated that Marlow Common’s production from its own clay source must have been around 150,000 bricks or terracotta products. The bricks (some called the ‘Marlow blues’) may be seen locally on and near the common and in Marlow town centre. However, the brickyard undoubtedly received clay from neighbouring extraction areas, and so its total production would have been much larger.