258 Scientific Proceedings, Royal Dublin Society. 



on the modern shore, are seldom seen projecting above the general 

 level of the pre-glacial one. In two general cases only does the 

 modern shore exhibit as plane a surface as the pre-glacial one ; 

 first, when the rocks are very soft and easily eroded ; and secondly, 

 when the seaward portion of the pre-glacial platform forms the 

 modern shore. 



The cause of this is to be found in the much slower advance 

 of the sea during the raised-beach period. It had then, in extend- 

 ing the upper margin of the platform, to undermine a cliff, in 

 most places over 100 feet high. At the present day it has 

 only to remove the 12 feet, more or less, which represents the 

 difference in level between the recent and pre-glacial shores. The 

 former is, as a consequence, much less mature than the latter ; or, 

 in other words, it is reduced somewhat less below high-water 

 mark at the present day than the pre-glacial platform was below 

 high- water mark at the time of its completion. 



In measuring the height of the raised-beach it was found 

 impossible to obtain a datum which could be used everywhere and 

 at any state of the tide. In some places the high water of mean 

 or ordinary spring-tides was available ; in others, the upper growth 

 limit of Balanus and Fucus was used ; or again, where the rocks 

 have been sufficiently eroded, the inner edge of the present 

 shore-platform was employed. Measurements made from this 

 last line to the corresponding margin of the pre-glacial platform 

 are particularly useful, as they serve to indicate the amount of 

 elevation of the beach. Owing, however, to the want of maturity 

 of the present shore, they are likely to give an under-estimate of 

 the elevation. 



Near Ballinglanna Cove in Clonakilty Bay the pre-glacial plat- 

 form was found to be about 10 feet above the present shore (see 

 PI. XXIX.). In a small bay, five furlongs east of Howe's Strand 

 Coastguard Station (Courtmacsherry Bay), the inner edge of the 

 pre-glacial platform is 10 feet above the corresponding part of the 

 shore-platform ; and a similar difference of level was found a quarter 

 of a mile east of Ballycroneen Coastguard Station. 



A number of observations, taken with reference to high-water 

 at ordinary spring-tides, showed that the exposed part of the pre- 

 glacial platform was generally about 5 feet above this line. 

 Details are given in the sequel. 



