332 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1917. 



doubtedly do so, but with regard to the 100-foot beach, Mr. W. B. 

 Wright states that it is apparently entirely unknown in Ireland. 

 There are, however, a few traces of its occurrence. 



On the Horn, west of Dunf anaghy, opposite Tory Island, is a well- 

 developed rock shelf with some flat stones and pebbles, backed by an 

 old deposit of blown sand, now cemented into sandstone in places. 

 The height of the shelf is about 70 feet; sand was banked against 

 the old cliffs for another 20 feet or so. Above the shelf the rocks were 

 not water worn. Just above Templebreaga Arch there was a distinct 

 shelf visible in section. In places at the level of the shelf was some 

 sand bedded at a low angle, the stratification planes marked by 

 pieces of fiat shale. 



Farther west I know of no traces of this beach, but the country 

 has not been thoroughly explored. In southwest Donegal I could 

 find no trace of it whatever. East of Horn Head, Professor Hull 

 mentions a beach at a height of 75 feet at Malin Watch Tower, in 

 Inishowen, and in his " Report " General Portlock refers to three sets 

 of old sea caves in the chalk cliffs of County Antrim, at heights of 

 12, 25, and 100 feet. South of this the 100-foot beach appears to 

 be entirely wanting, and this is doubly strange because the neighbor- 

 hood of Belfast abounds in quiet sea loughs suited for its preserva- 

 tion, which have been thoroughly explored. I will return to this 

 point later. At Dublin a rock shelf which occasionally appears at 

 a height of 25 feet may be the representative of the 100-foot or 50- 

 foot beach of Ulster, since the 25-foot beach has descended to a level 

 of 15 feet by the time it reaches Dublin and this shelf is much older. 

 It may be preglacial, but Kinahan stated (1878) that "About 35 years 

 ago or more (i. e., 1840) it (the 25-foot beach) was very conspicuous 

 along the cliffs (near Kingstown), but all traces of it have since 

 been obliterated; also in places at Bullock, Dalkey Sound, and at the 

 north end of Killiney Bay. 



A glacial flood-gravel terrace bordering the coast in the loughs of 

 Londonderry district may be referable to the 100-foot beach. Ac- 

 cording to Mr. Kilroe it gradually rises inland from about 50 to 125 

 feet, averaging about 75 feet above sea level. He says, " The mate- 

 rials have evidently been distributed by flood waters issuing from 

 receding glaciers over the valley floor and the low T ground bordering 

 the coast during the final disappearance of ice from the regions." 

 It is separated from the present shore line in many places by the 

 25-foot beach, which terminates against it in a well-marked cliff. At 

 the mouth of the glens of the Muff and Castle Rivers are great allu- 

 vial fans of fine sand and clay at a height of 50 feet above the sea. 



Beaches at a level of 30 feet or less above the present high-water 

 mark are of far more extensive occurrence. Often they form flat 

 plains a mile or more in width, which may constitute the necks con- 



