Holyhead Island, on W. side of Anglesey isl., and forming part of co. of Anglesey, 9658ac. (1325 water), pop. 10,131; is separated from Anglesey by a narrow strait, dry at low water, and crossed by a causeway with an arched water-way. The island is 8 miles long and 3½ miles wide, and is for the most part barren rock, ending on the N. coast in a large headland containing many caves. On the South Stack Rock, off the NW. point of the island, is a lighthouse 91 ft. high, with revolving light (Stack) 197 ft. above high water and seen 20 miles.

(John Bartholomew, Gazetteer of the British Isles (1887))