bruce wrote:

Basically I need to know how well sandstone will hold up as the stone
used in a waterfall.

Look at any number of ancient European churches. Sandstone is an often used
building material. It doesn't wear nearly as well as granite, but it
should last _years_ in a waterfall - assuming you aren't subject to
freeze/thaw cycles. If it freezes, the erosion will be greatly
accelerated.

--
derek