154 The hish Naturalist. July, 



the South of Ireland" — Quart. Journ. Geol. Soc, 1862, p. 378. 

 He postulates an original land-surface of Carboniferous rocks 

 high above the present one. He vSeems to assume that the 

 well-marked contortions which affect the rocks now accessible 

 to observation died out towards the top, and left a plane 

 sloping gentl}' to the south, and still more gentl}^ to the east. 

 Whether the plane might have been an un wrinkled surface of 

 deposition or a peneplain it is not necessary to discuss. 

 Granting the existence of such a surface, the earliest streams 

 would naturall}' flow from north to south. As time went on, 

 these would maintain their right of way if, as is probable, thej^ 

 retained sufficient fall ; but the east and west geological 

 structure would lead to the formation and extension of large 

 tributaries in the softer belts, whose waters would be trapped 

 by the primary valleys and carried to the sea, as at present. 



It is not surprising that an explanation of such simplicitj'' 

 and beauty should have held its ground for so long. The 

 hypothesis of underground movement, which had been 

 rejected so decisively by Jukes in i86t, was put forward b}^ 

 Hull in 1878 {Phys. Geol. and Geogr. of Ireland, first ed., p. 177). 

 His reason for not accepting Jukes's explanation was the non- 

 coincidence between the northern streams and the southern 

 diversions. But such a reason is of no weight in the case. 

 Rivers do not mark time in that fashion. Every water- gap 

 tends to travel with the stream, owing to the erosion of its 

 upper off corner. The tendency at Cappoquin, for example, 

 would be for the southern ravine to shift slowly to the east, 

 as the waters flowing from the west would impinge with special 

 force on the north-eastern corner of the bend. Geologists, 

 however, seem to have received Hull's criticism with indiffer- 

 ence, judging b}^ the estimate which is still set on Jukes's 

 great paper. 



There were certain difficulties of detail which I encountered 

 while engaged in the task of re-constructing the original land- 

 surface of the south of Ireland. These difficulties led me to 

 attempt the modification of Jukes's explanation of the river 

 courses. Although the attempt was not successful, I did not 

 lose faith in his theory as a general explanation, even when I 

 discovered at the end of 1899 that the present junction of 

 the Bandon and Brinny at Down dan iel Castle had been effected 



