460 PREHISTORIC EUROPE. 



by bog or peat of quite recent formation, which passes into 

 alluvium along the course of the Keiloge river, but is liable to 

 be flooded at spring-tides, showing, as Mr. Hardman is inclined 

 to think, still more recent oscillations of the sea-level. If, now, 

 we tabulate these results, we have the following succession of 

 changes : — 



1. Land-surface of wider extent than present. 



2. Submergence of land to a depth of not less than ten feet below the 



present limits of high- water. 



3. Eetreat of the sea ; land of wider extent than now. 



4. Re-submergence of land, not reaching more than two or three feet 



below present high-water mark. 



5. Retreat of the sea ; wider land-surface. 



6. Perhaps a very recent change of sea-level ; sea advancing. 



Amongst other examples of submerged trees and peat upon 

 the coasts of Ireland are those of Wexford Harbour, Youghal 

 Harbour, Clonea near Dungarvan, Courtmacsherry Bay, Dun- 

 worley Bay, Tralee Bay, and Kilcredane Point, at the mouth of 

 the river Shannon. 1 Eaised-beaches are also well developed, 

 the two lowest corresponding probably to the two postglacial 

 raised -beaches of Scotland. The upper one occurs at an aver- 

 age height of about 35 feet or more above the mean level of the 

 sea round Ireland ; the lower one at about 20 feet above the 

 same datum-line. But their heights vary according to the posi- 

 tion of the terraces, which in the estuaries and some of the bays 

 tend to rise to a somewhat higher level, just as we found was 

 the case with the raised-beaches of Scotland. The lower ter- 

 race, being the more recent, is necessarily better marked than 

 the other. It is of variable breadth, and often backed by cliffs, 

 at the base of which appear old sea- worn caves ; while isolated 

 stacks of rock rise up from the terrace itself. Here and there 

 natural and artificial sections reveal the structure of the raised- 

 beach, which in some places is largely composed of gravel 



1 See Mem. Geol. Survey Ireland : Explanation of Map, Sheets 104, 113, 

 103, 102 ; Sheets 140, 141, p. 16 ; Sheets 160, 161, 171, 172, p. 49 ; Sheets 

 194, 201, 202, p. 27 ; Jukes's Manual of Geology, 3d edit. p. 740 ; Kinahan's 

 Geology of Ireland, p. 264. 



