# How do chalk cliffs form? **URL:** \ **Category:** Factual Questions\ **Created:** [April 11, 2007, 4:39pm UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658 "2007-04-11T16:39:08Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [April 11, 2007, 4:39pm UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658/1 "2007-04-11T16:39:08Z")
Take the White Cliffs of Dover, for example. 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? ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [April 11, 2007, 4:54pm UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658/2 "2007-04-11T16:54:52Z")
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. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [April 11, 2007, 11:25pm UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658/3 "2007-04-11T23:25:22Z")
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](http://www.newyorker.com/reporting/2007/03/12/070312fa_fact_mcphee) is online. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [April 12, 2007, 12:26am UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658/4 "2007-04-12T00:26:53Z")
No, I haven’t seen it. I’m British, and I’m not sure it’s easily available over here, but I’ll have a look. Thanks for the suggestion. ---
**Author:** ![Barrington](https://avatars.discourse-cdn.com/v4/letter/b/278dde/32.png) [@Barrington](https://boards.straightdope.com/u/Barrington)\ **Post date:** [April 12, 2007, 1:43am UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658/5 "2007-04-12T01:43:06Z")
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. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [April 17, 2007, 10:48pm UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658/6 "2007-04-17T22:48:06Z")
So, the sea was once higher than the cliffs are now? ---
**Author:** ![Great\_Dave](https://avatars.discourse-cdn.com/v4/letter/g/46a35a/32.png) [@Great\_Dave](https://boards.straightdope.com/u/Great_Dave)\ **Post date:** [April 17, 2007, 10:55pm UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658/7 "2007-04-17T22:55:31Z")
Also, glacial rebound-- as the weight of all the ice has been lifted, the crust springs up. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 17, 2007, 10:59pm UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658/8 "2007-04-17T22:59:22Z")
[QUOTE=Peter Morris] 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? [/QUOTE] 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. Flint is made of sponge. ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [April 17, 2007, 11:06pm UTC](https://boards.straightdope.com/t/how-do-chalk-cliffs-form/399658/9 "2007-04-17T23:06:30Z")
[QUOTE=Peter Morris] So, the sea was once higher than the cliffs are now? [/QUOTE] 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](http://www.amazon.com/Map-That-Changed-World-William/dp/0060931809) 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.