CHAP. XIII.] PLEISTOCENE EPOCH. 275 



group of mariiie sands and gravels either in Ireland or 

 England as " Interglacial," that is to say, they are not 

 justified in regarding such beds as belonging to a phase of 

 Pleistocene time which was distinct and separate from the 

 epochs when Boulder-clay was formed. In Ireland, as in 

 England, there appear to be two groups of Glacial deposits, 

 an older and a newer, each including Boulder-clays and 

 gravels ; and the sands and gravels which occur at low 

 levels on the eastern coast and contain marine shells are 

 closely connected with the sandy Boulder-clay which over- 

 lies them. 



Non-Glacial Deposits. Baised beaches occur at many 

 places, especially round the northern half of Ireland, but 

 there is much difference of opinion regarding their number 

 and relative levels. Mr. Kinahan describes two distinct 

 and well-marked beaches, 1 a lower at or below 12 feet from 

 high- water mark, and a higher between 20 and 25 feet ; 

 but Professor Hull states 2 that the level of the 20-foot 

 terrace declines southward, so that between the mouth of 

 the Boyne and the north shores of Dublin Bay it varies 

 from 8 to 3 or 4 feet, and along the south shores the ter- 

 race cannot be identified, as it merges into the present 

 strand. Possibly this local declination is due to a change 

 in the position of the "head of the tide," as Mr. Kinahan 

 suggests, and the Dublin beach may belong rather to the 

 12-foot terrace. 



No ancient river-gravels containing Palaeolithic imple- 

 ments have yet been found in Ireland, the Welsh hills and 

 glaciers having apparently formed a barrier to the migra- 

 tion of man at that time. The mammoth and many of its 

 congeners have, however, left their remains in some of the 

 caves of southern Ireland, and the inland lakes and bogs 



1 " Geology of Ireland," p. 252 et seq. 



3 " Expl. of Sheets 102 and 112 of Geol. Survey of Ireland/' 1875, 

 p. 69. 



