A pug mill used for clay preparation was supposed to have the clay in a
barrel and have rotating knives to break up the clay (although I have never
seen one of these there are numerous contemporary illustrations). The only
similarity would be the horse walking around in a circle.

Maybe what was being thought of is a puddler which is similar to a Chilean
mill where a circular depression is excavated and a horse drags a set of
tongs or rakes around the depression which is filled with gold baring gravel
and water. The agitation separates the gold from the clay. The rakes are
attached to an arm which pivots around a stake in the centre of the puddler.


There is an excellent guide to mining terminology put together by Neville
Ritchie and Ray Hooker in Australasian Historical Archaeology Vol 17.

Iain Stuart
Principal, Archaeology and Heritage Management
HLA-Envirosciences Pty. Ltd.