298 



Proceedings of the Royal Irish Academy. 



margin of the great lobes and the location of the obstructing bastions are • 

 inserted in the map (fig. 4).^ 



The remarkable sand-tvact of Magilligan may represent the re-sorted 

 moraine of this Scottish lobe thrown down after a retreat from its furthest 

 position, while from the same source may have been similarly derived the 

 material forming the raised beach (25 foot) upon which the sand dunes, &c., 

 now rest. 



Fig. 4. 



Map illustrating the re-advance of the Scottish Ice. Doited line denotes marijin 

 of ice ; comb-line the Ballymonej" moraine ; arrows give direction of ice- 

 tlirusts. K. = Knocliliiyd ; S. = Benevenagh ; T. H. = Inishowen Head ; 

 By. = Ballynioney ; M. = Moville ; L. = Londonderry ; S. = Strabane ; 

 P. D. = Pennyburn Depression ; B. 0. = Biirngibbagh overilo-w ; L.B. = " Lake 

 Bnrndennet " ; C. D. = Culdaii Depression. Scale— 20 miles = 1 inch. 



The existence of a lake in Lough Foyle, discharging its surplus waters 

 into Lough Swilly, demands a retreat of the Donegal ice to a position at least 

 south of the line of the " Pennyburn depression." The extension of the 

 terracic deposits up the Burngibbagh valley, for a slight distance beyond its 

 confluence with that of the Taughan, suggests that, at the period of the 

 re-advance of the Scottish Ice and of the formation of "Lake Toyle," the 

 " Burngibbagh channel " was in operation ; that " Lake Burndennet " was 

 still in existence, though about to be abandoned; and that the edge of 



'■ I arrived at the above couclusion on the evidence here submitted some six years ago, 

 and presented it to the Cardiff meeting of the British Association in 1920. Tliough 

 Professor P. F. Kendall, who has accompanied me over part of the ground, and to whom 

 I outlined all the evidence, regarded the deduction as sound, Dr. A. R. Dwerryhouse 

 at that time refused to entertain it. The strength of the view is therefore enhanced by 

 its recent adoption in Dr. Dwerryhouse's paper already quoted. 



