15 Pt'oceedings of the tloyal Irish Academij. 



surface is frequently brown does not suggest a modern origin. It is to be 

 hoped that further observations may be carried on in this locality. Tliere 

 is no doubt that the Pliocene sea invaded many lowland areas in Ireland, as 

 in England, and that subsequent elevation played its part in the rejuvenation 

 of the streams. We know that in England this elevation measured at least 

 800 feet. 



The pre-Glacial beach traced by Messrs. H. B. Muff (now Maufe) and 

 W. B. Wright' over so wide a stretch of the Irish coast-line, and since 

 recognized in the west of England, lies close to the present sea-level. It 

 represents a time when there was a pause in the fluctuations in the amount 

 of land exposed above the reach of wave-action. But its occurrence along 

 the sides of the drowned valley of Cork Harbour shows that considerable 

 submergence of the coast had taken place before this stationary stage set in. 

 At an earlier epoch, the submergence may have been far greater, and the pre- 

 Glacial beach may mark a pause in the succeeding upward swing. 



The late Pliocene or post-Pliocene movement of elevation enabled some of 

 the streams to cut new channels in the slopes exposed by uplift to their 

 action. Other streams merely recovered the submerged portions of their 

 former mature valleys, which were thus restored to them from beneath the 

 sea. This fact provides an explanation of the occurrence of mature and 

 immature valleys on the same slopes side by side. 



Possible Preservation of the Foothills by Cretaceous Strata. 



While the above considerations offer an explanation of the youth of many 

 of the pre-Glacial trenches among the Leiuster hills, another cause may have 

 widely operated in preserving the Ordovician and Cambrian foothills, at very 

 different levels, from denudation. Evidence is rapidly accumulating as to the 

 immense amount of Upper Cretaceous strata that has been lost to us in compara- 

 tively recent times. Mr. A. J. Jukes -Browne'' boldly carries the Senonian sea 

 right across the Irish midlands. We may be inclined to question such an 

 invasion, owing to the probability that extensive patches of Upper Carboni- 

 ferous strata remained on the midland surface down into Cainozoic times. 

 But the enormous quantity of Cretaceous flint in the south of Ireland, and its 

 abundance off the west Irish coast,' indicate the justice of Mr. Jukes-Browne's 

 main contention. Large unworn flints are thrown up at the present day on 



' " The pre-Glacial raised beach of the south coast of Ireland," Sci. Proc. fi . Dublin Soc, vol. x 

 (1904), p. 250. 



' " The Building of the British Tales," 3rd ed. (1911), p. 333. 



' G. A. J. Cole and T. Crook, " On rocks dredged from the floor of the Atlantic," Mem. Gaol. 

 Surv. Ireland (1910), pp. IS, 22, &c. 



