S98 PEOCEEDINGS OF THE OEOIOGICAX SOCIETY. [JunO 18 



be seen to be furrowed by the rain into gullies and channels a foot 

 or more in depth, full of fine soil. All large limestone districts, both in 

 Ireland and elsewhere, are, as everybody knows, always full of caverns 

 and all the lesser rivers continually sink at one spot and reappear 

 at another after subterranean courses through such caverns, of some- 

 times several miles in length. In the country between Ennis and 

 Galway, it is often difficult to decide upon the connexion which 

 the detached streams of running water, that just show themselves 

 here and there in partial valleys at the surface, may have one with 

 another. 



Still, making every allowance for the efficiency of the action of the 

 weather to lower the surface of a limestone country, and extending 

 it in a lesser ratio to ground where its mechanical action operates 

 alone, I am fully aware that it will have rather a startling effect on 

 some persons' minds, to be called on to believe that mere rain and 

 other atmospheric influences can have washed away a thickness of 

 some hundreds of feet of rock from off the surface of a whole country. 

 It is evident that, if the explanation, for the formation of the ravines 

 of the Blackwater, Lee, and Bandon be a true one, it must be ex- 

 tended over the South of Ireland generally, and applied to those of 

 the Shannon, the Barrow, and the other rivers. Neither will it stop 

 there ; for if true for this country, it will be true for all other lands. 

 I can only say that the truth of the explanation has so forced 

 itself on my own mind that it will, I think, remain a conviction 

 until I hear from some one a better explanation of the facts than 

 that which I have here laid in outline before you. 



The time required for such an action to have accumulated such an 

 amount of effect is, of course, vast beyond all human effort at con- 

 ception. The South of Ireland, however, seems to have been ex- 

 posed as dry land to the atmospheric influences ever since the close 

 of the Palaeozoic Epoch, with the single exception of the depression 

 which it suffered beneath the sea during the Pleistocene or Glacial 

 Period. 



However long the duration of that Glacial Period may have been 

 it is clear that it was comparatively short, and the effect of marine 

 denudation during that time comparatively trifling in modifying the 

 form of ground previously elaborated. 



The time that has elapsed since the Glacial Period seems also to 

 have been comparatively short, inasmuch as we have still upon the 

 surface of many of the rocks the marks of ice-action not yet obli- 

 terated by the weather. Whether, however, we are to take as the 

 units of comparison between these times and those which preceded 

 them thousands, hundreds of thousands, or millions of years, or any 

 other conceivable quantity, I do not now pretend to discuss. 



D. Application of this Explanation to the Ravines of the Shannon 

 and the Barrow, Nore, and Suir. — I will now assume the approximate 

 truth of the following history: — -After the subaqueous formation 

 of the great sheets of the Upper Palaeozoic rocks over the whole of 

 Ireland, the subterranean forces began to act upon them, bending 

 them into the curves in which we now find them. 



