250 Proceeding& of the Royal Irish Academy. 



Louo-hermore Bridge doubtless represents an earlier position of the ice- 

 margin. The lake held up in the upper part of the Burntollet valley was 

 drained by a channel north of the hill of Glenconway. But little cutting 

 had taken place before a retreat of the ice-front freed the lower col to the soutli- 

 west of this hill, and the overflow, intaking at about 660 feet, O.U., and 

 falling south into the Fore Glen, was formed.^ 



The ice, in its retreat from the Eoe valley and behind the liills of 

 Glenconway and Loughermore, halted for some time at Holly Hill, to the 

 west of Dungiven. Here it deposited as a marginal accuinulation the belt of 

 irregular mounds of stratified sands and gravels forming conspicuous features 

 in the landscape.' 



A later pause in the retreat is represented by the morainic mounds and 

 the series of short, parallel ridges at Moys' running towards the Eoe. The 

 gravel mounds at Sistrakee Top, in alignment with these and some three 

 miles W.-S.-W. of Moys, probably form part of the same great morainic 

 accumulation. They were traced at least one mile farther west, to the 

 south of Legacurry. A still later halt is represented by the hummocky 

 country running from Catmill, S.-E. of Faughanvale Bridge, to the S. of 

 Walworth Wood and from near Tamlaght Bridge to the MuUagh.* 



The position of the ice-front at this stage is indicated on the accompanying 

 map (Stage 3, PI. VIII). The more striking features of the marginal 

 phenomena at this period are the great lakes of Gortin, Glenelly, and Claudy 

 and the large transverse valley of the " Inver Channel," which carried the 

 waters of the lakes on the south side of the Sperrin Mountains into the series 

 of lakes on the north side. 



{A)— Fourth Stage. 



A retreat of the ice-edge off the western shoulder of Slievebeg threw -'Lake 

 Gortin" into confluence with "Lake Glenelly"; the "Barnes Gap" outlet 

 thereby became inoperative. The confluent lake now drained by the " Inver 

 Burn " channel. Its level was determined by the intake of the latter, just 

 below 600 feet, O.D. In conformity with this lowering of " Lake Gortin," the 

 stream dischar-ging into it the surplus waters of " Lake CuUion " no longer 

 ceased to cut to just below the 800-foot level, i.e. the height of the Barnes 



' The curious delta-like form at the entrance of this valley into the Fore Glen, and 

 brought out by the oOO-foot contour, is in part a corrom. 



- Reference is made to these gravel hills in the Geological Survey Memoir, Sheet 18, 

 p. 23. 



3 Mr. J. R. Kilroe described these features (Belfast Nat. Field Club, up. cit., p. 656). 



* The name of the short ridge on the west side of Roe Park demesne, Limavady, 



