>Have such deposits been found? If so they would also have to be bleedin' obvious or else the builders wouldn't have found them in order to use them.<
Quite.
It never fails to amaze me how facts such as the one you quote, and the possible worked bluestone now lying at the bottom of the sea, are so easily ignored in order to substantiate someone's latest theory.
As with 'lying by omission', there should be a phrase for hypothesizing without due consideration ;-)