While U.S. stocks gained ground, the grind higher in prices that dominated trading through late April has given way to more back-and-forth swings.

WSJ: Blue Chips Reclaim Some Lost Ground

The National Trust thinks the internal workings were substantially altered in about 1840 to allow the mill to grind wheat, having previously ground oats.

BBC: Cumbria's Acorn Bank Mill grinds first flour for 70 years