494 Kinahan — Formation of RocJc-hasins. 



fall than running water, it migiit have excavated the gut ; for the 

 ice would first have slid over a fall near the east end of the gut and 

 scooped out a hole, and, as the fall was cut back, the hole would 

 become longer and longer till at last the gut we now find was 

 formed. 



Lackavrea (b on Map, PL XVIII.) is a high steep hill close to the 

 lake; and if ice, sliding down a steep slope, can cut into a rock, 

 there ought to be a hollow at its base. On looking at the chart 

 this is found to be the case, as the soundings suddenly change from 

 about 20 to from 60 to 80 feet ; this deep is marked c on Map, PL 

 XVIII. The hills, N. and N.W. of Carn Seefin, approach close to 

 the margin of the lake, and at their base there is also a deep. In a 

 similar manner the deeps N.W. of " The Old Lough " would be 

 formed by the ice from the hills on the north, and the deeps, S.W. 

 and S. of Inchagoil, by the ice plunging over the hills that now 

 appear as either islands or shoals. 



In the valley of the Owenfough, the rocks have the appearance 

 as if a large glacier once flowed out of that valley into the valley 

 of Lough Corrib, and Lough Corrib extends in an elbow-shaped bay 

 towards it.^ 



Might not this elbow be due to the Owenfough valley glacier 

 plunging over the bar of rock, on which Oughterard now stands and 

 cutting out the rock. In a similar manner the glaciers, coming 

 down the E. and W. valley north of Knockaleeky, which lies a little 

 west of Eoss (p on Map, PL XIX.), would cut out Ower Bay (q on 

 Map, PL XIX.) ; and the glaciers out of the valley at MoycuUen (s 

 on Map, PL XIX.) Moycullen Bay (e on Map, PL XIX). 



On the east side of the Lough similarly circumstanced bays occur, 

 but they could not be pointed out except on a geological map, being 

 now filled with bog or alluviura. Another fact in favour of the 

 Lough Corrib Yalley, being an ice-scooped rock basin, is, that in the 

 north-west portion of the lake, which is nearly surrounded by hills, 

 and where the primary stri^ must be deflected considerably by the 

 different mountains, the islands are scattered irregularly about, while 

 in the rest of the lake, which is open to the X.E., nearly all the 

 islands have a similar bearing to the primary striee : as if their 

 nucleus were originally "Tors" or "Roches Moutonnee" in the ice 

 stream.'* 



1 have now laid before my readers the facts remarked in connec- 

 tion with the " Eock basin " of Lough Corrib, and which seem to sug- 

 gest the following conclusions :— That the extent of the lake in the 

 limestone country has increased in those places where the water and 

 the atmospheric agencies combined could act on the limestone;^ but 



^ This ■would be much more marked on a geological map, on which the bog and 

 alluviura were coloured, as then the original dimensions of this part of the lake could 

 be seen. 



2 The lie of the islands can be better seen on a larger map. 



2 Although its superficial extent has increased in some places, it really has been 

 greatly curtailed, for many of the large bays, as previously mentioned, are filled up by 

 bog and alluvium. These could not be defined until the geological maps surrounding 

 the lake are published. 



