Mixing cement

[Bruce]

Probably crushed alluvial gravel.

** Posted from **

[Bruce]

She thinks you're hilarious. She's right. ;-)

** Posted from **

[Spamlet]

An experiment gainsayers might like to try before getting any more cherty:

In this Wiki entry:

the picture caption reads:

"Pebble beach made up of flint nodules eroded out of the nearby chalk cliffs"

Try editing it to read: "Pebble beach made up of *gravel* eroded out of the nearby chalk cliffs."

Let us know how you get on.

Anyhow, all irrelevant to an overall very handy thread.

Cheers, S (One time geologist. Anybody in the market for my old rock samples? Ah: don't tell me: ballast!)

[Rod]

Up to a point.

Alluvium is from running water, n'est pas? I was thinking if it was from a glacier it would be moraine. But then I tried looking it up and found the word 'till'.

I can't help feeling that most river deposits are somewhat rounded (but not, I agree, as rounded as sea stuff). Where the stuff I mentioned was truly sharp.

But you are probably right.

[The Natural Philosopher]

moraines are made of till.

I live on one.

Clay here, with flint and chalk well down underneath.

Up the road, gravel pit, where they sieve out the sand (very smashed flint), and a fair amount of less smashed flint, which is called gravel or shingle.

The difference between chert, flint, and most sand is one of context: all are basically silica.

Gravel/shingle/sand is a loose term that really boils down to fragment size..however in the building and gardening trade, flint gravel is just called 'gravel'. and you tend to get e.g. 'granite shingle' used to describe smashed up granite chippings..

although technically 'limestone gravel' exists, its not called that here: Its called MOT type I.. ;-)

Really it may or may not be. If you hit e.g. N walees you will find scree slopes of very sharp stuff indeed. It only needs a storm to carry a bit away in water, and lay it down for it to become a shingle or gravel bed.

it takes a lot longer to weather to rounded pebbles or 'soft sand'

[Spamlet]

How rounded pebbles and grains are, depends on how many times around the sedimentary cycle from beach to rock and back again they have endured. For hard materials like silica the time scales involved are almost unimaginable. Real experts can look at your sand/gravel deposit and work out exactly where it came from and how it got there and just how long ago the individual grains were created, and indeed where they to were made. For a perfect natural concrete look at some Hertfordshire 'pudding stone', the individual rounded beach pebbles look as if they are separate from the matrix, but the whole breaks clean across - that is, if you are strong enough to break it at all. There is some in my garden...

Ah the heady days of Rutley, Read and Watson.

S