 The mouldstone, filled with rainwater, is just above and to the right.The mouldstone is the best field evidence for a blowing house; they are large blocks of granite with a flat top containing a rectangular hollow recess into which the molten tin was poured to be cast into ingots.The moulds vary in size and shape, the largest known from Dartmoor being that from Upper Merrivale at , and the smallest square at Longstone.