I know that chalk is formed from and billions and jillions of tiny sea creatures that died and sank. What I don’t understand is how come the cliffs tower over the sea like that.
Did sea level used to be much higher, and the present clifftops were underwater?
Has there been some geological activity under the cliffs which push the chalk upwards?
Also, I’ve heard that chalk cliffs are sort of sandwich like, with alternate layers of chalk and flint. Where does flint come from? I’ve heard that it is possible to match layers of flint in the Dover cliffs to corresponding layers of flint in the French cliffs. Is that right?
It is most likely related to the retreating glaciers that have been retreating for the past 20,000 years, combined with tectonic activity and good old fashioned eroision.
Someone been reading John McPhee’s recent New Yorker article on the subject?
If you haven’t, then it’s worth a look, though it’s fairly waffly and I can’t remember whether it addresses these specific questions in detail. Alas, only an abstract is online.
Chalk is quite recent, geologically speaking. Where it forms uprisings, such as in the Yorkshire and Lincolnshire Wolds (and, presumably, the white cliffs of Dover), it’s due to a combination of previously-high sea levels and - mostly - warping of surface strata.
Flint nodules crystallise out of the material that becomes the chalk - it is composed of silicon that comes from the bodies of marine organisms such as sponges, echinoids, urchins, etc.
In a way - but more likely that the chalk was once beneath the sea and was slowly shoved upwards, then eroded.
If you’re interested in learning more about this, I can’t recommend The Map that Changed the World highly enough. It’s about the guy who first realised what caused all this stuff, and how he worked it out. It’s an interesting historical tale too, and very well written.