The district is served by the Dun canals.
The occurrence of Ordovician rocks was first established by Dun at Tomingley, 33 m.
The rath or dun from which the town is named remains as one of the finest in Ireland.
The family of O'Clery, to which three of the celebrated " Four Masters " belonged, were hereditary 011aves (doctors of history, music, law, &c.) attached to the family of O'Donnell; while the " Book of the Dun Cow " (Lebor-na-h Uidhre), one of the most ancient Irish MSS., was in the possession of the O'Donnells in the 14th century; and the estimation in which it was held at that time is proved by the fact that it was given to the O'Conors of Connaught as ransom for an important prisoner, and was forcibly recovered some years later.
These men were specially Service trained at Dehra Dun in the work of surveying, and entered Tibet with a strong wooden box with a specially concealed secret drawer for holding observing instruments, .a prayer wheel with rolls of blank paper instead of prayers in the barrel on which observations might be noted, and lamaic rosaries by the beads of which each hundred paces might be counted.