1862.] JTTKES ^EIVEE- VALLEYS. 393 



highest beds of the coal-measures, the rocks of the district became 

 affected by movements acting from below, which gradually bent them 

 into great longitudinal synchnal and anticlinal folds, and that the 

 denuding agencies subsequently acted on these folded rocks, and 

 eventually produced the present surface of the ground. It is possible 

 that, as one resu''-t of the disturbing action, some of the upper beds 

 were immediately raised into dry land, and began to suffer from 

 both marine and atmospheric denudation. The two actions of denu- 

 dation and disturbance may therefore have been in simultaneous 

 operation throaghoat an unknown pedod of time. It is, however, 

 clear that the disturbing forces eventually ceased to operate, and the 

 folding of the rocks became as complete as we now find it. The 

 denuding agencies, however, are still in operation, and have never 

 ceased to operate upon every portion of the country as long as it has 

 been at or above the level of the sea. 



The denudation wiU of course act upon the rocks unequally, in 

 accordance with the inequalities in their chemical composition or 

 physical structure, and will of course produce a form of ground in 

 accordance with these inequalities. The surface of the country, then, 

 while it originates from denudation alone, will yet be modified by the 

 previous action of disturbance which has placed differently consti* 

 tuted rocks in different positions and at different levels, where the 

 denudation found them when it succeeded in wearing down to them. 

 In this district, then, at all events, the internal disturbing forces 

 have had only an indirect effect, while the external denuding action 

 has been the direct agent in the production of the form of ground. 



There is, however, nothing exceptional in the circumstances of this 

 district, and the very same arguments might be applied, mutatis 

 mutandis, to all other countries. 



C Projposed Eocplanation of the Formation of the Transverse 

 Ravines. — It would appear from the foregoing considerations, that 

 the only possible way in which the transverse ravines on the present 

 courses of the Eivers Bandon, Lee, and Blackwater could have been 

 formed is by the erosive action of running water over dry land, — ^in 

 other words, by river-action. 



But we have already seen that no rivers could now commence to 

 eiode these ravines, supposing them not to exist and the adjacent 

 ground to retain anything approaching to its present form and rela- 

 tive levels. "We are, therefore, driven to the conclusion that the com- 

 mencement of the erosion of these ravines took place upon a surface 

 that had a different form and level from those which the present 

 surface has. 



I had been for many years at fault for an explanation of the 

 origin of these ravines, when, during the last winter, I was led to 

 perceive a connexion between them and some of the lateral brooks 

 which come towards them from the higher slopes on the north ; and 

 I will now describe this connexion for each of the three rivers. 



a. River Bandon. — A little below the point where the Eiver 

 Bandon commences to turn from its wider E. and "W. valley and to 

 cut by a ravine into the ridges on the south side of that valley, it is 



