654 



[Proe. B.N.F.C., 



An interesting circumstance, bearing upon the relation of the 

 Boulder-Clay of the third to that of the second stage, was noticed 

 in the bank of a small western tributary of the Roe, 3)^ miles south 

 of Limavady. There, pieces of reddish compact highly calcareous 

 Boulder-Clay are enclosed in a more gravelly non-calcareous clay, 

 showing that the former had been laid down prior to the latter ; 

 and, that the ice carrying the latter, while not entirely erasing the 

 former from the valley, broke it up here and there, and carried it 

 along as it did ordinary boulders and other detritus, to be 

 redeposited, as described, during the period of melting. 



In the Bann Valley erratics of the several varieties of Slieve 

 Gallion rocks strew the ground, and are enclosed in the Boulder- 

 Clay from which the materials in many gravel-pits have come. 

 The numbers of those rocks increase proportionally, southward, 

 by Garvagh and Kilrea, as mentioned above, a fact which indicates 

 a northerly movement of their once containing ice, as already 

 remarked. Confirmatively of this a dark grey highly calcareous 

 clay, studded with basalt and other boulders, is to be seen in high 

 steep stream banks at Gorran Bridge, about 3 miles north by west 

 of Garvagh, and at Bovagh House, just north of that town. The 

 clay is identical in character with that derived from the glacial 

 waste of Carboniferous limestone, which seems to me to point to 

 the Carboniferous area south of Maghera as its origin. 



BOULDER-CLAY OF FOURTH STAGE. 



Directly covering the rock on the basalt plateau west of the 

 Bann, and often found as a thin layer upon previous Boulder- 

 Clays is a loose-textured mixture, though when of considerable 

 thickness it is hard and tough at the bottom. A study of this 

 mixture convinces one that it is a Boulder-Clay of comparatively 

 local origin, though frequently mixed with untravelled materials, 

 quite local. It seems to mark the decline of general glacial 

 conditions, when accumulations of snow, neve, and ice lay upon 

 the higher ground and were subject to periodical meltings and 



