262 Proceedings of the Royal Irish Academy. 



Mullaglishuraven and Altihasky, and so into the Movola Eiver. 'I'his lake 

 and its outlet continued to exist until the direetioti of the normal drainage 

 via the Owenkillew Eiver was opened. It was therefore in existence during 

 part of the second and third stages of retreat from the Sperrin Mountains. 



The moraiuic featui-es were encountered at intervals along the floor of the 

 depression towards the south-west, occurring either as fine billowy belts, or 

 projecting as isolated mounds and ridges above the flat turf bog. East of 

 Mulderg, they again assume considerable proportions, e.g. the large 

 moraine, irregular and hummoeky, forming the ridge appropriately named 

 '■ The Murrins." Other large ridges of the same character cross the wide 

 expanse of turf country between the lower slopes of Mullaghcarn and 

 Castle Kock, e.g. Bauck Hill. Similar ones cover the tract south of 

 Mountfield, extending as far east as Milltown and Loughmacrory ; this large 

 lake is held up by moraines. They are ridged up on the hillsides of the 

 small recess above Mountfield. The country from Mountfiekl to Drumnakilly 

 is covered with seoies of these ridges, here extremely finely displayed. Very 

 interesting and significant is the mode of behaviour of the ice, as shown by 

 the moraines. In the great majority of cases, when an obstruction stood in 

 its path, though such barriers were only small hills rising but 100 or 200 feet 

 above the general surface of the country, the ice was held up in front of the 

 obstacle, but swept along on either side. This is illustrated by the following 

 hills: — Laght Hill, Crockancor, Scalp, Slievemenagh, Muluafj^e and the low 

 ridge running west from MuUaslin Gap ; the lobes thrust through the gaps 

 iu the Beleeviiamore range, as sketched above, are mereh' instances on a far 

 larger scale. These moraines have seriously interfered with the drainage. 

 Numerous lakes and lakelets are impounded in intermorainic depressions; 

 indeed, all the lakes of this extensive area are true morainie lakes.'^ The 

 orisiu of the large and small undrained areas of bog,- abounding in this 

 region, is doubtless to be sought in the similar impounding of the drainage 

 by the moi-aines. The thick turf lying between the larger moraines has 

 most probably in places completely buried the lesser and intermediately 

 situated mounds and ridges, while only the summits of others, somewhat 

 higher, project as small eminences above its surface. 



Numerous sections show the nature and the mode of arrangement of the 

 materials of these ridges and mounds : these need not be detailed here.^ 



'The largest are L. Cam, L. Fingreau, L. Mallon, Black L. aud the pretty 

 Loughmacrory. 



- Oue of the lai'gest is that of Cloghfiu, several square miles in extent ; a few morainie 

 mounds project as islands above the turf surface, their position marked by a few houses 

 and cultivated fields. 



^ One of the best is at Mullaslin Gap. 



