SOUTH-WEST IRELAND. 187 



terraces, as shown in section (a, a, fig. 24, PI. IV.), 

 would be found at the sides of an alluvial flat (#, b) 

 in which flowed a river (c) ; furthermore, the river 

 probably would be in a supplementary flat bounded 

 more or less by sloping gravel cliffs. 1 Advocates of sub- 

 ferial denudation have pointed to similar flats and ter- 

 races to prove what this agent can do ; as they seem 

 to believe that only rivers can form sloping terraces. 

 It has, however, been shown that the sea is capable 

 of forming them ; and not only them, but the supple- 

 mentary flats bounded by gravel cliffs, which mark, 

 not a river flat, but the margin of a gradually-rising 

 estuary bottom. Even the gravels owe in a great 

 measure their origin to sea action ; as the detritus 

 carried down into the estuary by the rivers is a baga- 

 telle when compared with the quantity of sand and 

 gravel that was formed by the sea from the washing 

 and grinding-up of the moraine-drift. And similar 

 features would be displayed by the elevation of most 

 estuaries ; namely, a terrace at the head of the valley, 

 with minor terraces at a similar level in those places 

 where streams or rivers flowed into the old bays, with a 

 shelf or cliffs marking the old sea-margin; also, slop- 

 ing terraces from the terminal terrace to the mouth 



1 If the land were to rise 200 feet, the terraces at Inishbarna would 

 be about 130 feet above the water, while those at the end of the bay 

 would be nearly 200, giving a fall of the slopes of about 70 feet in nine 

 miles, about equal to the fall of the terraces in the upper part of the 

 valley. 



