July, 1902. 153 



GEOGRAPHICAI. EVOI.UTION IN CORK. 



BY J. PORTKR, B.H. 

 [Read before the Cork Naturalists' Field Club, May T5th, 1902. J 



Thk greater portion of the county of Cork presents a stage of 

 downward erosion, at which a fairly close correspondence has 

 been developed between the larger surface features and the 

 underground rock- structure. The more or less obdurate Coal 

 Measures, which would have interfered with this development, 

 have been practically wiped out all over the district to the 

 south of the Blackwater. The sandstones and slates belonging 

 to the Old Red series are overlaid by Carboniferous beds, 

 which are generally of a less enduring nature, being either 

 shaly slate to the south or almost pure limestone to the north. 

 The close east and west folding which these rocks underwent 

 during the Hercynian movements, has led to the production 

 of a set of alternately resisting and enduring cross-country 

 belts, formed by the bevelled edges of the exposed strata. The 

 main drainage trunks tend to occupy the synclinal Carbon- 

 iferous belts, their tributary streams seaming the flanks of 

 Old Red Sandstone ridges between. 



Both geologists and ordinar}^ observers have long since 

 noticed the peculiar easterly drainage of the longitudinal 

 valleys. Their contained w^aters are in every case led south- 

 -wards through narrow courses before the sea is reached, 

 although the broad Carboniferous straths are continued to the 

 east without break. The first attempt to afford an explana- 

 tion of the southerly diversions on Huttonian principles was 

 made by Jukes. He describes the facts of the case at Cappo- 

 quin, on the Blackwater, with all his accustomed clearness, in 

 the Explanatio7i to Sheets 176 and 177, p. 8 (date 1861). He 

 reviews the evidence regarding underground disturbance as a 

 diverting cause, and decides unhesitatingly against it (p. 13). 

 The explanation which he framed, and which was suggested 

 by the junction of the Brinny with the Bandon {ExpL to Sheets 

 194, 201, 202, p. 12), was fully worked out in his classical 

 paper " On the Mode of Formation of some River- valleys in 



