[19] Introduction to O'CURRY, _Manners and Customs of the Ancient Irish_, 1873, i., p. cccxxix. The various kinds of monument were the _Derc_, the _Fert_, the _Leacht_, the _Duma_, the _Cnoc_, and the _Carn_. The _Derc_ was a hollow, a pit, or hole, dug in the ground; in fact, a simple grave. The _Fert_ was a rectangular chamber, composed of stones set upright, and covered horizontally with flags; in a word, a kistvaen. The _Leacht_ seems to have been a larger-sized kistvaen, a cromlech or dolmen, but a single upright stone was also called a leacht. When a number of persons were buried in a single mound, then a stone was set up in commemoration of each round the tumulus or cairn. A good specimen may be seen beside the road to Widecombe from Post Bridge. The cairn has been almost levelled, but the ring of stones remains. The _Cnoc_ was a rounded, sugar-loaf mound of earth, and the _Duma_ was a similar mound raised over a kistvaen. The _Cairn_ or _Carn_ was a mere pile of stones, generally made over a grave, but sometimes having no immediate connection with one. Here is a curious passage which will explain why some cairns contain no interments:-- "The plunderers started from the coast, and each man took with him a stone to make a carn, for such was the custom of the Fians when going to plunder or war. It was a pillar-stone they planted when going to give a general battle; and it was a cairn they made this time, because it was a plundering expedition.... Every man who survived used to remove his stone from the cairn, and the stones of those who were slain remained in place, and thus they were able to ascertain their losses."--_The Book of the Dun Cow._ Sometimes, after a battle, when it was not possible to carry away a body, the head of the man who had fallen was buried by his friends under a cairn, because the ancient Irish were wont to carry off heads as trophies; but to violate a cairn, even when raised by a foe, was regarded as sacrilege. On Dartmoor, in addition to prehistoric antiquities, numerous rude stone crosses remain; some of these, if not all, indicate ways, and were employed as landmarks. Only one bears an inscription, "Crux Siwardi." The whole of the moor, in the stream bottoms, is seamed with streamers' "burrows" and deep workings. It is not possible to fix their date. Throughout the Middle Ages stream tin was extracted from Dartmoor. Fresh activity was shown in the reign of Elizabeth. Beside the mounds may be seen the ruins of the old "blow-house," where the tin was smelted, and very probably among the ruins will be found the moulds into which the tin was run. I postpone what I have to say on the tin-working to a chapter on that topic in the ensuing portion of my book, on Cornwall. Books on Dartmoor:--