394 PEOCEEDINGS Or THE GEOLOGICAL SOCIETY. [June 18, 



joined by a large brook, called the Brinny, wbich cbmes into it from 

 the northward. This brook springs from the summit of the Old Eed 

 Sandstone ridge which strikes across Ireland from Sheep's Head to 

 Knochadoon Head (see Map). It cuts deeply into the south side of that 

 ridge, and, soon after it issues from it on to the valley, it receives some 

 large brooks from the west, and then runs through another ridge, by a 

 deep glen, to its jimction with the Bandon Eiver. The river-valley 

 below this junction is in fact merely a continuation of the valley of 

 the Brinny, with the same features which it has above the junction ; 

 and the Brinny receives the Bandon from the west out of the main 

 longitudinal valley as a tributary, nearly in the same way that other 

 brooks come into it as tributaries from the west, out of the smaller 

 longitudinal valleys, while none but the most insignificant streams 

 faU into it from the east. (See Explanation of Sheets 194, 200, and 

 201 of the Geological Survey of Ireland.) 



We are therefore led to look upon the valley of the Brinny as the 

 primary valley, that was first formed, or at least first commenced, by 

 the running of a stream from the do'ninant ridge on the north, south- 

 wards towards the sea, and that that valley intercepted all the 

 drainage of the country that ultimately ran towards it from the 

 west. 



It will be recollected that it was stated at p. 382, that the anti- 

 clinal and synclinal folds of the rocks strike E. and W., but that their 

 axes generally rise towards the "W., so that ..the bottoms of the lime- 

 stone troughs were pinched out, and the lower rocks (the Old Eed 

 Sandstone) formed the higher ground in that direction. "While, then, 

 the beds dip almost invariably either IST. or S. at high angles, the 

 whole mass of the contorted rocks has had, as it were, a gentle tilt 

 downwards towards the east, or upwards to the west, sufficient ap- 

 parently to turn the drainage of the surface generally in that direc- 

 tion as soon as any longitudinal valleys began to be formed on the 

 surface. It is for this reason that all the larger lateral or N. and S. 

 valleys receive their principal tributaries from the west, while that 

 of the country to the east of them is carried still further eastwards. 



The Brinny Brook, then, first commencing .to . run over a surface 

 considerably above any part of the present surface, formed a lateral 

 !N". and S. channel before any of the longitudinal E. and W. valleys 

 and ridges became prominent, and thus marked out the winding 

 southerly course it has ever since followed. As the longitudinal 

 valleys were gradually formed by atmospheric denudation, the run- 

 ning waters of this brook always; cut down across the intervening 

 ridges faster than the general denuding agency lowered the longi- 

 tudinal valleys ; so that it was continually receiving more and more 

 of the western drainage, and turning the water down its own trans- 

 verse ravine. 



JSTone of the other lateral brooks springing from this Old Eed Sand- 

 stone ridge for a considerable distance to the westward had equal 

 power with the Brinny, until we reach the Eiver Hen, which, in like 

 manner, cut through the ridges to the south, and formed a basin of 

 drainage of its own distinct from that of the Brinny and the Bandon. 



