S96 PROCEEDINGS OF THE GEOIOeiCAL SOCrETT. [Jiuie 18, 



geologist will consider as more than a temporary and accidental 

 occurrence which may produce, or may have produced, its own 

 modifying effects, according to its power and duration. 



c. Biver Blackwater, — If we look northward from the ravine of 

 Dromana towards Cappoquin, where the Blackwater turns at right, 

 angles towards the south, we find two very large brooks issuing into 

 the valley from the far loftier Old Eed Sandstone ridge on the north, 

 which is in fact one of the flanks of the Knockmealdown Mountains. 

 One of these brooks is that which comes out opposite Lismore, Si- 

 miles to the north-westward of Dromana ; and the other is the Glen- 

 shelane Eiver, which comes out about three miles north by east of 

 Dromana. These brooks may have very readily united their waters 

 somewhere about the northern end of the Dromana ravine. 



There is also a third lateral valley which descends the Old Eed 

 Sandstone ridge still further to the eastward, and now brings the Eiver 

 Finisk to the Dromana ravine ; but I believe that this formerly 

 crossed the Dromana ridge further to the east, where there is a de- 

 pression in the ridge opposite its glen. It was gradually deflected 

 into the Blackwater, in consequence of its not being able to wear 

 down its channel over the r?dge fast enough to keep it below the 

 bottom of the gradually sinking limestone valley. 



The ravines of Dromana and Camglass, and the others between 

 Cappoquin and Youghal, I believe to be the remnants of the channel 

 of a river that ran southwards over the old loftier surface of the 

 ground from the dominant ridge of the Knockmealdowns on the 

 north. As in the previously cited instances, I suppose this river to 

 have deeply trenched aU the rocks in its course; and, as the whole 

 country suffered from atmospheric degradation, and became lowered 

 in consequence, it still kept eatiag deeper into the land, so that its 

 channel was always below the level even of the limestone valleys, 

 and always kept open the passage across the ridges on the south, so 

 as to turn all the drainage it received into that passage. 



The section in fig. 5, PI. XX., will serve to illustrate the expla- 

 nation I propose with regard to the Blackwater. In this the lower, 

 darkly coloured part represents the present ground, with the rocks 

 lying in their present position beneath the surface, — ^tlie heights, for 

 the sake of distinctness, being drawn to a scale of four times the 

 lengths. The fainter tints above suggest the former extension of the 

 rocks removed by denudation. Of these I suppose the uppermost, 

 lightest- coloured parts to have been probably removed by marine 

 denudation, which produced a surface approximately represented by 

 the line AAA. The part below that, which is coloured with tints of 

 intermediate strength, will give us the approximate form of the 

 ground over which I suppose the lateral brooks to have rrn down to 

 the i:ea, before the commencement of the formation of the longi- 

 tudinal valleys. I believe that the line AAA marks out the limit 

 of the marine denudation, and that all the iatermediate part between 

 that line and the present surface of the ground has been re- 

 moved by atmospheric degradation alone. So long as the district 

 remained dry land, .the features first impressed upon it by the atmo-. 



