Chalk: 2. Brighton to London

Cross section through the geology (more or less) between Brighton and London (from Geology of East Sussex: Wikipedia)

It’s a shame I struggled with my packing, leaving me sleep deprived as well as behind in my planning and research. I might have taken more photos out of the train window to share here. Hooray for Wikipedia!

A journey for me is a multidimensional entity. Every railway cutting gave clues to a story told by the rocks. The white chalk of the South Downs (coloured lime green in the picture above) can sometimes be seen. Scientists have found that it is more than 66 million years old. I will be telling more about it later.

Where the chalk is covered by vegetation, careful observation reveals plants that only grow in alkaline chalky soils, such as wild clematis.

Emerging out of the long dark Clayton tunnel, the vegetation changes. Young shoots of acid loving bracken could be seen emerging from amongst other fresh green spring growths. The sandstones and clays of the Kent and Sussex Weald are of older rocks which in Brighton are hidden deep under the chalk.

The train sped past Gatwick (after letting people off and on) then before we got to Croydon, suddenly the white chalk was back!

Geologists have measured the angles to the horizontal of each of these strata wherever they can be seen. They have also identified fossils which are unique to all of the different layers. This has proven that the South and North Downs were one and the same layer of chalk.

Chalk formed during the Upper Cretaceous in hot tropical seas. It is made from the dead chalky shells of tiny sea creatures, their remains falling like snow to the seafloor. But something happened about 30 million years ago to lift up the sea floor. The chalk sea floor between Brighton and London was somehow lifted up, like a giant soufflé, and collapsed in the middle! The eroded middle resulted in the uncovering of the older layers underneath.

To learn more about the origins of our South Down soufflé is the purpose of my study trip. Of which more tomorrow!

<- Chalk: 1 | Chalk: 3. Tunnel Sous La Manche ->