These six standing stones, locally known as 'Cerrig yr helfa, ' not marked on the Ordnance Survey sheet, are in a line with one another on Mynydd Dyfnant. The tallest is 6 feet above the ground, the others are from 1 1/2 feet to 2 feet. The average distance between the stones is 10 feet. Though unhewn stones of the mountain, they appear to owe their positions to design. A seventh stone is just visible in the bog, into which it seems to have sunk. The direction of the line is north-east by south-west. -- Visited, 29th July, 1910.
There's something by Alex Gibson about the stones in v38 of 'Archaeology in Wales' (1998): "The Growing and Shrinking Stone Row of Cerrig yr Helfa, Mynydd Dyfnant, Powys".