Chalk

This chalky digression could be dated to the lump of chalk from Yaverland noticed at reference 1, but is more properly dated to the recent piece in the Guardian at reference 2 about water levels in the River Test, where I read that there are only around 200 chalk streams in the world, with three quarters of them in southern and eastern parts of England. But why was this so? I reminded of this by the piece at reference 3. So off I went.

I now know that: '... Chalk is a fine-textured, earthy type of limestone distinguished by its light colour, softness, and high porosity. It is composed mostly of tiny fragments of the calcite shells or skeletons of plankton, such as foraminifera or coccolithophores...'. Calcite is a very pure form of calcium carbonate, to be distinguished from its cousin, magnesium carbonate. This last a cousin of magnesium sulphate, aka Epsom Salts.

Then that '... Much chalk was deposited during the Cretaceous Period of geologic time. It was a time of global high sea levels that began at the end of the Jurassic Period about 145 million years ago and the beginning of the Paleogene Period about 66 million years ago. During the Cretaceous, warm waters of epeiric seas, seas that flooded continental crust during sea level highs, existed in many parts of the world...'.

You get chalk in many places in the world, but given that formation involves the sea, not central Asia. But you get chalk streams where you have a layer of near surface chalk, good for holding water, on top of an impermeable layer, perhaps clay. The streams spring from the junction of the chalk with the clay, hence the springs in and around Epsom and the Hogsmill of reference 3. I have yet to run down why particularly England, but maybe its geological history - with clay being under the sea at about the right time - is not that common. While the Somme is a large chalk stream in northern France.

On the other hand, chalk being porous, means that it is sometimes a reservoir for oil and gas, as in Texas, as snapped above, from reference 6 below.

And a little to the north you have the Monument Rocks of Kansas, for which see reference 8. An inland version of the White Cliffs of Dover.

I also spared a thought for water. Presumably the total amount of water in and around the earth does not vary that much, so high sea levels presumably correspond to warm periods when not much water is locked up in the ice of Antarctica, Greenland and elsewhere.

PS 1: a note for geeks, regarding the 'shtml' suffix at reference 6. According to Bing's AI assistant: 'SHTML stands for Server-Side Includes HTML. It is an HTML file that contains server-side instructions, allowing dynamic content to be included in web pages. This file type is similar to ASP (Active Server Pages) and is used to enhance web pages with dynamic features such as visitor counters, calendars, or other server-generated content'. Which seems plausible enough. Both references 6 and 7 are badly infested with advertisements.

PS 2: and a new to me way of filtering out time-wasters. I presume that respectable outfits do not ride on the back of gmail. Or perhaps you can pay Google to make such riding invisible.

References

Reference 1: https://psmv5.blogspot.com/2025/07/trolleys-916-917-and-918.html.

Reference 2: Southern Water applies for permission to draw water from rare chalk stream: Environment secretary urged to stop drought order that could damage the ecology of River Test in Hampshire - Helena Horton, Jasper Jolly, Guardian - 2025.

Reference 3: A short history of the Hogsmill River in Ewell - Epsom Civic Society Newsletter No.180 - 2025.

Reference 4: https://en.wikipedia.org/wiki/Chalk_stream.

Reference 5: https://en.wikipedia.org/wiki/Chalk.

Reference 6: https://geology.com/rocks/chalk.shtml.

Reference 7: https://geologyscience.com/rocks/sedimentary-rocks/chalk/.

Reference 8: https://en.wikipedia.org/wiki/Monument_Rocks_(Kansas).

Reference 9: https://www.scdiscoveries.com/.