342 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



Mountain, near Enniskillen, and elsewhere tumuli or cairns referred 

 to the bronze age have been built and subsequently covered by sev- 

 eral feet of peat ; this shows that the change occurred not earlier than 

 the bronze age. For the reasons stated above, peat formation prob- 

 ably commenced earlier in the forests than on the bare ground. Re- 

 cently the climate appears to have become drier, for in eastern Ire- 

 land the bogs are ceasing to grow. 



From the raised beaches, the estuarine and lacustrine deposits, and 

 the peat bogs I have now constructed a fairly connected account of 

 the history of Ireland since the melting of the last great ice sheet. 

 The remaining superficial deposits can be dismissed briefly; they 

 fit readily into the sequence and so far entirely confirm it, but they 

 provide little that is new. 



The Irish caves have been frequently investigated and have added 

 to the list of Irish Pleistocene fauna, but their bearing on the climate 

 is small. More important are the sand dunes which occur at very 

 many places on the Irish coasts, and are noted for the neolithic 

 hearth floors with flint implements, pottery, etc., which are exposed 

 among them from time to time. Detailed descriptions of these pre- 

 historic remains were given by Mr. W. J. Knowles in 1889, 1891, and 

 1895 ; the implements are neolithic in age, and the presence of pot- 

 tery points to a fairly late section of neolithic times. The sand dunes 

 frequently rest on the flats of the 20- foot beach, and are consequently 

 younger than that submergence, and they probably originated in the 

 fir-forest period, when both elevation and dryness were favorable to 

 their formation. But to render them habitable they must have been 

 fixed by vegetation, probably during the moist period of the upper 

 peat. The subsequent readvance of the sand may be due to the slight 

 desiccation which has caused the cessation of growth in the bogs of 

 east Ireland. 



LAND TO THE WEST OF IRELAND. 



The almost complete absence of postglacial raised beach deposits 

 over the greater part of western and southern Ireland suggests that 

 the district was elevated to such a height that even the submergence 

 of the 100-foot beach failed to leave any traces above the present 

 shore line. This elevation was also inferred by Maxwell Close (1867) 

 from the configuration of the deeply indented west coast. The con- 

 tours of the latter at a depth of 200 feet present far more resem- 

 blance than the present shore line to the east coast of Ireland. The 

 central plain of Ireland also is lower in the west than in the east by 

 about 200 feet. He also pointed out that the axis of movement of the 

 " Irish ice," which passes very near to the coast in southwest Done- 

 gal, necessitates a considerable extent of land to the westward. Re- 

 cently Messrs. Cole and Crook (106) have remarked that rocks indi- 



