148 Proceedings of the Royal Irish Academy. 



Donegal from that in the county Londonderry. The former, Tvhich is- 

 very small, is part of the peninsula of Inisho"^en. 



" The ccimtT DeiTv portion of the district is characterized by the 

 extensive plains that border Lough Foyle ; the lowest of which is a 

 raised beach, bounded on the sea-side by large tracts of reclaimed 

 land or intakes." 



(p. 6.) — " The high ground in the east of sheet 12, with its- 

 contiauation in sheet 6, is underlaid by the basalt which forms the 

 great Tertiary plateau of the counties Antrim and Derry. The 

 boundary of this Tolcanic area is here, as in other parts of the district, 

 often characterized by bold, precipitous cliffs, which, towards the 

 north, assume magnificent proportions, and are accompanied by huge 

 landslips of comparatiTely recent date. The rugged masses thus torn 

 away, rise sometimes in sharp pinnacled forms in front of the steep 

 face of solid rock, and are separated from it by a gap, strewn with 

 blocks that have fallen in large numbers on either side. 



" The bold outline, which thus denotes the boundaiy between the 

 Secondary and Tertiary formations, passes northwards and eastwards, 

 with a wide sweep into sheet 6, accompanied by a gradual descent 

 towards the coast. Here, at the east of Umbra, it consists of a 

 steeply-receding cliff of chalk and basalt, about 500 feet in height, 

 supporting a mass of boulder clay, which stands piled up against the 

 escarpment for a height of nearly 300 feet." 



(p. 7.) — " East of Umbra the boundary of the basalt follows the 

 coast-line for a short distance, bending out below the sea, within a 

 mile of Downhill ; while beyond this point, and as far eastward as 

 the locality just named, nearly perpendicular crags, composed of 

 basalt, with some beds of ash, overhang the shore, skirted for half 

 their height by an accumulation of blown sand, resting on boulder 

 clay, and in some parts barely upholding ponderous semi-detached 

 masses of rock, which seem ready to fall from their position. 



" From Downhill eastward to Castlerock, the cliffs directly overlook 

 the sea, having a more irregular and rugged outline, owing to the 

 constant and frequently violent action of the waves, which are at 

 the present day hollowing out caves in the basalt. Similar openings, 

 standing at a somewhat higher level, and dating back to the period of 

 the adjacent raised beach, occur in the chalk between Downhill and 

 Umbra ; whilst, in some instances, as at Backaunaboe ( ' the tether- 

 stake'), a little east of Downhill railway station, the conditions seem 

 to point to a continuous drilling action carried on from that day to 

 the present. The above name is given to a sharp sea-stack, composed 



