242 Proceedings of the Royal Irish Academy. 



Duugiveu.^ represents the lacustiiue deposits formed in "]>ake Beuadj'." 

 Possibly belougiug to this stage, though doubtfully I thiuk, are the warps and 

 highly calcareous clays containing a few small pebbles, aud buif or reddish in 

 coloui", exposed in the good sections, 20 feet high, in the brick-field at or 

 near MuUane, north-east of Limavady.- Alore probably of this stage are 

 the beautifully cuixent-bedded sands obsen^ed just east of Castle Bridge, near 

 the main road from Limavady to Unngiven, also the pebbly stratified deposit 

 at "Walk Mills (three miles S.-E. of limavady), though these are in part 

 morainie. 



Indicating the position of the ice-front at one stage of the retreat is a 

 ridge of sand and gravel which commences at an altitude of 850 feet, O.D., on 

 the flanks of Keady "FTill and crosses the valley of the Curly Eiver, finally dis- 

 appearing as a series of scattered morainie hillocks near the Largautea Burn. 

 This ridge was attributed by J. E. Kilroe^ to an en-glacial river, which, as a 

 temporary aqueduct, flowed some 150 feet above the present Curly bed. A 

 stage in the retreat, in part probably later than this, is represented by the 

 morainie country runuiug from the debouchure of the Owenrigh Eiver in a 

 north-easterly direction to Duugiven, and continuing with interruptions as 

 an iri'egular strip of country along the foot of Donald's Hill, past Ardmoie, 

 to the south-east of Limavady, where the constituent sands and gravels are 

 well exposed. 



Uence, there would appear to have been a progressive shrinking of the ice 

 to the east and west from the line of the basalt escarpment, and to the south 

 aud north from the Speriin Moimtains. Slightly lower levels characterize 

 the lakes on the western and northern sides, so that all the direct overflows 

 across this great watershed, from the western end of the Sperrin Mountains 

 to Bene\enagh on the north, with the single exception of the " Murder Hole," 

 the most northerly of the series, fall either west or north. The position of 

 the ice margin at this stage, with the corresponding impounded lakes, is 

 represented on the map (Stage 1, PI. VIII). 



(b) — Semnd Stage. 

 In the succeeding stage (Stage 2, PL VIII) the most striking feature is the 

 vast extent of the deep lake held up in the vaUey of the GleneUy Eiver. 

 Prior to the opening of the Inver Burn channel, this lake had a length of 



' E.g., S. of Boviel, at " v " of " JRiver Roe " of one-inch O.S. map, in the left bank of 

 the river. Here the section, some 70 feet high, consists almost entirely of sand, with an 

 occasional layer of pebbles. 



- These with more probability are the deposits of " Lake Foyle," fonned at a later 

 stage of the glacial period. 



3 Belfast Kat. Field Club, p. 656. 



