Dr. John Evans's Address to Section C. 413 



boulder clay, limestone gravel or middle drift, and extensive bogs, 

 so that tbe subjacent rock is but occasionally seen. In several places 

 detached bosses of Old Eed Sandstone rise through the limestone, 

 and there is also good reason for believing, with Professor Hull, that 

 the whole of the area was at one time covered with the upper 

 members of the Carboniferous group, including the true Coal-measures, 

 of which unfortunately but small patches remain, and those upon the 

 margin of the plain. From the absence of the Upper Palajozoic, 

 Mesozoic, and Cainozoic formations over the area. Professor Hull has 

 arrived at the conclusion that the surface remained in the condition 

 of dry land, while that of England was being submerged beneath 

 the waters of the sea, over the bed of which nearly all these forma- 

 tions were deposited. To a certain extent, however, he leaves it an 

 open question whether some of the Mesozoic strata which occur over 

 the north-east of Ireland may not have been deposited over the 

 centre and south. The amoimt of denudation over this central area 

 has, no doubt, been such that the chances of even Professor Judd 

 finding traces of these later deposits appear at first sight to be but 

 small ; but whether the whole of this vast amount of denudation is 

 due to the wasting influence of rain, rivers and other sub-aerial 

 agents of erosion, is a question which I venture to regard as at all 

 events open to discussion. It appears to be the case that in some 

 parts of the North of Ireland the whole of the Upper Carboniferous 

 beds had been denuded before the deposition of any Permian strata, 

 as these are deposited immediately on the Carboniferous Limestone ; 

 and if this amount of denudation had taken place in pre-Permian 

 times in the north, there seems a possibility of the same having been 

 the case in Central Ireland. If so, it is possible that some traces of 

 the later deposits may yet be found on the central plain. Certainly, 

 if we are still to regard the White Chalk as a deep-sea deposit, the 

 Cretaceous rocks of the north-east of Ireland must have at one time 

 extended farther south than they do at present, and somewhere or 

 other there must have been shore deposits of that period formed 

 further south than the Upper Greensand of Antrim. The careful 

 investigations of Professor Judd have largely extended our knowledge 

 of the Secondary rocks of the western coast and islands of Scotland, 

 and he has been able to show that the Jurassic series of the Western 

 Highlands could not have had a thickness of less than three thousand 

 feet. It is therefore hard to believe that, with such a develoj)meut in 

 so closely neighbouring a district, the deposits of the same age in 

 Ireland can have been restricted to their present area. 



Professor Judd considers that the amount of denudation in the 

 Scottish Highlands since the Mesozoic and even the Miocene period 

 has been enormous, and that the great surface features of the High- 

 lands were produced in Pliocene times. It seems therefore possible, 

 if not probable, that so long a period of exposure to sub-aerial 

 influence as that assigned to the central plain of Ireland by Professor 

 Hull, would have resulted in a more uneven land surface than that 

 which we now find. At all events, the history of this remarkable 

 physical feature is one which is of high interest, and can hardly as 

 yet be considered as closed. 



