There is a brief description in Jeremy Butler's ever excellent Dartmoor Atlas of Antiquties Vol. 3 (1994):

"... a cairn supporting Emmet's Post, one of the series of pillars put up about 1835 defining the boundary between Lee and Shaugh Moors. The cairn, a substantial mound with slightly hollowed top, (9.0 x 1.2 m) now lies at the very edge of the encroaching clay workings."

It also gets a couple of mentions in Crossing's Guide To Dartmoor (1909) as a landmark - but probably more the post than the "mound" it stands on.