14 The Irish Naturalist. January, 



NOTES ON THE GLACIAL GEOLOGY. 



BY J. DE W. HINCH. 



The Glacial deposits of Lambay are most irregularly distributed, 

 the Boulder-clay often varying from over four feet to a few 

 inches in depth within a distance of a hundred yards, an irregu- 

 larity which, no doubt, results from the clay filling the hollows 

 in the Pre-glacial land surface — a surface which is being steadily 

 revealed by the cutting back of the north-western shore-line. 

 It is only on this north-western slope that any continuous depth 

 of Boulder-clay is to be found, the most satisfactory section 

 being that produced by the land-slip on the face of the cliff over 

 Saltpan Bay. Along this scarp, roughly the shore-line be- 

 tween Calico Hole and Broad Bay, occur a number of sections 

 of Boulder-clay of the tough brown type so familiar on the 

 lower slopes of the Dublin hills, and like that type crowded 

 with travelled stones and shell fragments, and overlying 

 smoothed rock-surfaces. Occasionally this brown type is re- 

 placed by a rather darker sort in which the pebbles appear to 

 be mostly limestone. The following rocks collected in these 

 north-western sections have been kindly identified by Professor 

 G. A. J. Cole : — Very common — Carboniferous limestone. Common 

 — Old Red sandstone, quartzite, chalk, flint, shale, Lambay por- 

 phyry, chert. Scarce — Ailsa Craig riebeckite-rock, hornblende 

 granite strongly resembling Tyrone type, biotite gneiss, decom- 

 posed ferruginous micaceous rock (probably lamprophyre), fine- 

 grained micaceous sandstone, compact igneous rock of felstone 

 type. 



The shell fragments though not rare are fragmentary, and in 

 poor condition, so much so that at first it looked as if none 

 were recognizable. Further search resulted in the following 

 list :— 



Mylilus, sp. Tellina balthica. 



Cardium edule. Iyittorina, st. 



Cyprina islandica. Turritella terebra. 



Astarte coiupressa. Pleurotoina turricula. 



A. sulcata. Balanus, sp. 



