Chalk Downs
The North Downs is a ridge of chalk hills - a geological band that runs from east to west. They run from Farnham in Surrey to the famous White Cliffs of Dover on the far-eastern side of Kent. Within this, there are two Areas of Outstanding Natural Beauty (the Surrey Hills and the Kent Downs). The North Downs are divided by rivers and valleys, including the Darent Valley. In the Darent Valley, the Downs are mostly made of chalk.
The North Downs chalk hills have long steep slopes, called escarpments, and thin soil which makes it difficult for plants and animals to grow and survive there.
Chalk
Chalk is a kind of limestone. It's mostly made up of calcium carbonate which comes from the shells of tiny sea creatures that died millions of years ago when Kent was underwater. The sea creatures' bodies built up on the sea bed and over time, they have been pressed together to make rock. The chalk limestone of the North Downs was laid down 65 million years ago!
This rock is sedimentary which means it is made up of layers. Chalk is porous, letting in water and other liquids, as well as being easy to break.
Quarrying
We know that chalk was mined in the Roman period. Chalk pits have been found at several sites including Lullingstone. These were found in places where the chalk was quite close to the surface, with only a thin layer of soil above it.
Many of the villas along the Darent Valley were built using chalk to mix lime and make mortar. Flint within the chalk was likely used to build walls.
Chalk Grassland
Chalk grassland, found in the Darent Valley, has thin soil without many nutrients. This means that plants with deep roots that need a lot of water can't grow as well in these areas. Instead, other plants like orchids are able to grow without competing with dominant lush grasses. The grassland is made up of calcium carbonate and is rich in lime. It drains well and is well-suited as a habitat for many snails. Every square metre of chalk grassland can support 40 different species including insects and butterflies.
Woodland
Chalky soil in the Darent Valley has also helped tree species grow without competition from other plants. Calcareous woodland is found where chalk is close to the surface of thin soil. Some of the species found in these areas include beech, yew and ash trees.
Activity Idea
GEOGRAPHY
Study a map to locate where chalk downland can be found in south east England. Find and highlight Farnham in Surrey and Dover in Kent which sit at each end of the ridge of chalk. Follow the North Downs area between these two places to understand the direction of the chalk through Kent and the Darent Valley.