280 Proceedings of the Royal Irish Academy. 



which coursed down the Grleiitoscher valley from the suout of the Glentogher 

 glacier, and which at a later stage flowed from the extra-glacial late ' held 

 up bj' the Foyle Glacier in the embaymeut at the head of the glen. It 

 probably also includes the remains of the boulder-clay which, well washed 

 and sifted, was swept off the hill-slopes and from the sides and floor of the 

 valley. 



Occasional "dry" valleys mark the progress of the withdrawal of the 

 ice from the Malin Peninsula. The largest of these is the deep and broad 

 glen which falls steeply eastward into Glentooskert. It discharged the 

 overflow waters of a very large lake impounded in the valley of the Keenagh 

 Eiver. A couple of small valleys on the sides of the hill to the north of 

 Maliu Town, falling east, are probably due to marginal drainage. Some water 

 also probably escaped eastward into the Portaleen valley. These channels 

 and others, as to the origin of which there can be less certaintj% agree in 

 denoting a recession of the ice westward and southward from this peninsula. 



The ice, which receded from the western flanks of Coolcross and Slieve 

 Suaght and the eastern shoulders of Bulbin, formed a large Mintiagh glacier. 

 This, at one stage of the retreat, held up a small lake to the south of 

 the King of the Mintiaghs, which drained northward by a small clmnnel. 

 By retreating southward, the Mintiagh Glacier was merged into the larger 

 Swilly Glacier, and a lake impounded in the broad valley of the Owenbeg 

 Eiver. The surplus waters of this lake were discharged by a large direct 

 overflow, which intakes just north of ilintiagh's Lough, and falls northward into 

 the- valley of the Clonmany Eiver. The lake surface stood at about 320 feet, 

 O.D., and attained its maximum extension just prior to its extinction, and 

 when the edge of this part of the Swilly Glacier swung from Liafin Hill, 

 passed BallymaganHill to Mouldy Hill and GoUau Hill. An earlier position 

 of the ice-front is marked by the morainic lidge at Fallask, along the north- 

 west foot of Crockuamaddy. For a brief period, prior to the disappearance 

 of " Lake Miutiagh," its overflow waters found escape by the valley near 

 Keeloges Bridge. 



" Lake Mintiagh " received the waters carried by a channel from a higher 

 lake held up in the recess W. of Scalp Mountain. 



Of slightly earlier data was the lake which was impounded in the valley 



ballast pit by the L. & L. S. Railway, just W. of the Carndonagh Railway Station, and 

 in the very good sections in the R. Don.agh, near this place. It is seen to consist of 

 diorite, schist, quartz, coarse and fine metamorphic grits, burnt and unburnt chalk-flints, 

 chalk, spheroidal basalts (very deeply weathered) and granite. (Barnesmore.) All the 

 pebbles are well rounded or sub-angular and clearly water-worn. 

 'The height of the lake surface was about 530 feet, O.D. 



