Note that the beam has no enclosed bearings, only simple, unrestrained pivots. The recoil from the beam hitting the clay would probably destroy an enclosed bearing quickly. I'd love to think that these primitive engineers designed it that way but the reality is probably a clay mill farther up the river that has its bearings beaten into splinters. It's still an ingenious way to avoid the complexity and frictional losses of the conventional waterwheel turning a shaft with embedded lifters.