1912-13] 653 



chalk and flint debris intermixed, and pieces of marl and Triassic 

 Sandstone probably. Further reason will be given for believing 

 that the melting succeeded rather than preceded the second stage 

 of glaciation.* 



THIRD STAGE OF GLACIATION. 



The ice which carried the Boulder-Clay belonging to this stage 

 of glaciation has left us by far the greatest collection of records. 

 Nearly all the glacial striae met with, are attributable to this system ; 

 some are noticeable on the summit of Lougheramore Hillf (1,070 

 feet above datum) and many in the lower ground, especially on the 

 basalt plateau ; and the prevailing direction is a little to the west 

 of north, with an occasional tendency to swing more to the westward. 

 At one point near Ballynacally More, three miles north of Garvagh, 

 the direction indicated is about 15 degrees north of west — which 

 is exceptional. 



The Boulder-Clay belonging to this stage is also interesting ; 

 and the evidence of ice-movement, derived from the erratics, 

 equally convincing. The contents of the Boulder-Clay point 

 almost wholly to a southern origin ; though, in the Roe Valley, 

 boulders of basalt predominate, near the escarpment, lessening 

 gradually as we proceed westward, and becoming rare, with a 

 preponderance of metamorphic boulders, on the valley sides west 

 of the Roe. 



One of the most interesting pieces of evidence, that the ice of 

 this stage moved northward, is to be found in the Largantea Valley, 

 east of Benevenagh, where debris of the Chalk, gathered up from 

 the outcrop northward from Keady, is strewn along the stream 

 course up to its head waters, but in decreasing quantity, while 

 chalk-flints may be picked up on the highest portion of the ground 

 there ; and I have found metamorphosed grit borne from the south, 

 at the summit of Benevenagh 1,260 feet above datum. 



*See note B at end. 



I" Memoir of the Londonderry District," pp. 52, 53. 



