"dpb" wrote in message
oups.com...
On Jun 6, 6:35 am, "C & E" wrote:
...

By previous posts this I gather that this is a mineral layer or a layer
of
hardpan subsoil. Would someone please explain.

http://en.wikipedia.org/wiki/Caliche_%28Mineral%29

(Google is your friend... )

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Ahhh, impure calcium carbonate! Yep, gotta be hard!