Sunday, 2 March 2008

Cliff Geology

Feeling fairly mobile today I decided on a short walk to where the latest cliff fall occurred, sometime around November last year. Along the bottom several Rock Pipits were obviously staking out their territorial claims.

I'm not a geologist but the formation of the beach and cliffs is fascinating. Stretching out in to sea is a pavement, or platform of chalk, that I presume is the result of previous thousands of years of cliffs being eroded to sea level.

At the base of the cliffs is a wide pebble beach, formed by the rounding, by the action of the sea, of the flints that occur in the eroded chalk cliffs.

When I arrived at the fall, the "extra white" chalk, that has yet to weather, shone out, and some of the defences against erosion hung forlornly down the cliff. The chalk layer that forms the cliffs is comprised of a sequence of mainly soft, white, very fine-grained extremely pure limestones. These rocks are mainly formed from the skeletal elements of minute planktonic green algae, associated with varying proportions of larger microscopic fragments of bivalves, foraminifera and ostracods. The planktonic coccoliths and many of the foraminifera (the planktonic species) lived floating in the upper levels of the oceans. When they died their skeletons sank to the bottom, combining with the remains of bottom living bivalves, foraminifera and ostracods, to form the main components of the Chalk.

In the face of the cliff layers of flints can be seen. They comprises a random mosaic of quartz crystals, only a few microns in diameter, interspersed with minute water-filled cavities. The silica was derived from the dissolution of the siliceous skeletons of sponges and other organisms and has been redistributed in the form of nodules during several stages of crystallisation.

Inside flints you can sometimes find a white or cream coloured soft powdery chalk inside flints. It is known to geologists as "flint meal". Fossils such as echinoids can be present within flints. Flint was a very important resource for our ancestors, as a huge variety of tools were crafted from it with great skill. The best tools came from certain types of flint, which often had to be mined. It seems either the blackest or whitest flint was best for tools, as most tools we have found are at one end of the spectrum or the other. Flint tools are extremely sharp, and can be up to four times sharper than a surgeons scalpel.
In later times flint was used extensively for building, providing a very resilient building material. Many buildings in Kent have some flint in their construction, including the oldest parts of several churches. Whilst these were the primary uses for flint, other uses included the knapping of flints for flintlock firearms, for road building, and in the making of stoneware.

I'm so used to photographing Fulmars from the top of the cliff that I'd forgotten how hard it is to get them in focus and in the frame from underneath, thank goodness for digital cameras! This one shows the flints protruding from cliff nicely, and some impression of the absolute mastery of the air that the Fulmar has.

As I'm sure you realise, I've raided various sites for the geological facts about the cliffs. The WEB has the potential to be the most wonderful educational tool.

No comments: