Burnard described the photograph as "stone ..... with circular cavities".
The remains at Week Ford are evidence of the tin mining industry which operated on Dartmoor until around 1939.
The stone with the circular cavities is a mortar stone. They were used for crushing the tin ore in a stamping mill. The cavities were created by the continual hammer of the stamping pole driven up and down by a waterwheel.
This appears to be a mortar stone at the upper blowing house.