Chaulesworth— Glacial Geology of North- West of Ireland. 255 



and the " Black Park channel " intaking at about 370 feet, O.D. Terraces 

 corresponding to these three overflows are clearly developed in the valley 

 10 tlie south of Dunnamanagh, and were produced as the deltas of the large 

 " Inver Channel" overflow.' 



The waters pouring by the large valley extending south from 

 Dunnamanagh into the large " Lake liurndennet " to the north of that village, 

 deposited tlieir detrital matter as huge terracic accumulations^ at and around 

 tliis place. The monndy accumulations of sand and gravel K of 

 Dunnamanagli" are manifestly tlie material irregularly dumped down on the 

 floor of this lake. In later stages the lake was almost choked up liy the 

 infilling of detrital sand and gravel.* 



The overflow of the lake by Bond's Glen (B.O.) is of great magnitude, and falls 

 N.-E. into the Faughan Valley, W. of Claudy. The extent of the down-cutthig 

 would appear to be about 70 or 80 feet, the channel having been initiated at 

 about 400 feet, O.D. The terraces in the lake above fall, in consequence, 

 through this height from 400 feet to 320 feet, successively newer terraces 

 forming at lower and lower levels in correspondence with the lowering of the 

 outlet. The terrace at Crockanore, formed as a delta of the " Windy Hill " 

 (W.H.) overflow, corresponds to this Bond's Glen outlet of "Lake 

 Burndennet." A recession of the ice-front of more than four miles was 

 necessary before the marginal drainage was presented with fresh means of 

 escape by the huge Burngibbagh valley. 



" Jjake Claudy " drained, as shown above, by two outlets, the " Feeny " 

 ( ¥.0.) and " Ballynioney " (B.O.) overflows. Not until the ice had retreated 



1 The location of the highest terrace has already been detailed. The "450" terrace 

 is very well developed among other places at Lisnaragh, at Claggan and around Hugheys 

 Lough, which lies in a hollow in the terrace. The lowest terrace occurs N.-W. of 

 Lisnaragh. Elsewhere it was largely destroyed during the later phases of the glacial 

 drainage ; indeed all these terracic deposits were later considerably modified by the 

 opening of the still lower channels, and the consequent rapid erosion of the earlier 

 deposits. 



"Streams " showing in places beds of stratified sand and gravel, sometimes 150 feet 

 tliick" (IMem. Geol. Survey, Sheet 17, p. 30). Tliis terrace, about 320 feet, O.D., in altitude, 

 is perfectly well developed about Dunnamanagh, extending along the sides of tlie valley 

 for almost one mile S. of this place. It occurs N.-W. of the village and extends as a 

 broad strip, almost half a mile wide, from here to Bunowen and Leitrim Hill- The latter, 

 completely surrounded by deltaic material, is composed of " solid," and doubtless formed 

 an island in the lake. 



^ These are especially well seen east of Fawney ; Duck Lough lies in a hollow between 

 tlie mounds. The irregular character of the surface is indicated by the iiOO-foot contour 

 of the one-inch O.S. map. These lake deposits also cover an extensive area to the north 

 of Fawney, at an altitude of something above 300 feet, O.D. 



"* The large pit in this terracic material at Downholme, near Dunnamanagh, sliows 

 well-worn shingle, chiefiy schist and of good size, clearly indicating the strength of the 

 current, . 



