You're right strazza and thanks for that. I always stand to be...

You're right strazza and thanks for that. I always stand to be corrected - more often than not:)

I must get back to studying my edition of geology for dummies but it should have been obvious to me that it is because the sand is 'coarser that it is more workable than shale/lime.

That is the good thing about this forum, by helping each other out we get the info right in the end.

#:>))