188 THE RIVER VALLEYS OF 



of the bay, with a river flowing in a valley, often 

 more or less flat, between the sloping terraces. While 

 the sloping terraces may be quite conspicuous, the 

 marginal shelves may be more or less obscure, as 

 they must be subsequently modified, or even obliterated 

 in places, by meteoric abrasion. When first these 

 sloping terraces were observed in the valleys of lar- 

 connaught opening to the west, we were inclined 

 to consider that the land had sunk more on the west 

 than on the east ; but afterwards, when such terraces 

 were found in valleys opening eastward, we were 

 forced to look for another explanation; and the theory 

 we now put forward is founded on the facts recorded 

 in the charts of different estuaries and bays, not only 

 in Ireland, but also in Scotland. 



The work done in Killary Harbour and Erriff 

 Valley since the ice left them may be thus sum- 

 marised. As the land sank, at the beginning of the 

 ie Esker-sea " period, the sea was clearing out part of 

 the boulder-clay from the valley, and in places doing 

 a little rock denudation. Part of the gravels and 

 other detritus was carried out to sea, but a consider- 

 able portion was left behind to fill up hollows, and 

 form a gently undulating bottom to the bay, and 

 sloping flats in the bays and broads. Subsequently, 

 as the land rose, the sea partly cleared out the 

 gravels it had previously redistributed, but left 

 terraces as monuments of its former activity. In 



