150 Proceedings of the Royal TrhU Academy. 



narrow neck "by wliicli tlie promontory is united to the mainland, 

 thougli ahout 8 miles from shore to shore, is formed of an old sea-hed, 

 which has been, elevated into land, certainly in very recent times, 

 and, in all prohahility within the period during which Ireland was 

 inhabited by Celtic tribes. It corresponds with the well-recognised 

 '25 feet raised beach' of our northern coast. This naiTow strip, 

 along which the railway from Londonderry to Buncrana is carried, 

 has an average elevation of fi'om 20 to 25 feet above Ordnance datum, 

 and only for a short distance, near Pennybum, is the level materially 

 exceeded, the ground i-ising to 50 or 54 feet above Ordnance datum, 

 or 41 to 45 feet above mean level." 



(p. 10.) — "Eut the island of Inishowen, thus constituted, seems 

 to have been itself a double island, owing to the existence of a second 

 narrow strait by which it was crossed at the period above referred to. 

 Between Culdaff Bay, on the east, and Trawbreaga Bay, on the west, 

 there stretches a low neck of alluvial land, deeply covered with peat ; 

 and, during the period of depression, this was overflowed by tidal 

 waters, as the old sea-bed, consisting of sand, silt, and gravel, well 

 seen in the neighbourhood, underlies the peat, which has gi'own over 

 the surface since its elevation into land. The highest level of this 

 alluvial tract is 50 feet above Ordnance datum, or 12 feet above high- 

 water of ordinary tides, and of this, probably, 10 or 12 feet consists 

 of peat. At its western end this strait communicated with the ocean 

 both to the north and south of Doagh Island, which is at present 

 connected with the mainland by a bar and sand-dunes forming the 

 shore of PoUan Bay. 



" (Xote.) — Dr. Sigerson (Proc. Ptoy. Ir. Acad., 2nd ser., vol i., 

 p. 212, bt seq.) has adduced historical evidence in confirmation of 

 the statement that Inishowen was an island, not only within the 

 period of human habitation, but within that of history. In the maps 

 of the Escheated Counties of Ireland (1609), of which facsimile copies 

 were taken at the Ordnance Office, Southampton, in 1861, a strip of 

 water is shown connecting the Foyle and the Swilly loughs across to 

 the north of the ' City of Derrie,' just where the raised sea-bed 

 occurs. Another stiip of water is shown, stretching from the ' Lake 

 of Loughfoile,' near Saint Johnstown, to the inlet of the Swilly, near 

 Castle Hill. Derry itself stood on an island before the last elevation 

 of the land as a strip of water, recently a morass, bounded the hill on 

 which the old city is built, on the west. Sigerson quotes passages 

 from the 'Annals of the Pour Masters,' of the dates a.d. 1211 and 

 1010, in which the name island is applied to the present promontory ; 



