A Walk along the Glacial Cliffs of Killincy Bay. 15 



the day on which its inhabitant abandoned this life, and a 

 valve of Lzicina was found still retaining its outer horn}' coat, 

 the so-called "epidermis." A list of the species found in the 

 boulder clay is given by Mr. Praeger at the end of this 

 account. 



Singularly hard and coherent as the boulder clay is, it 

 readily breaks down into a fine mud on boiling in water ; the 

 impalpable material of which it chiefly consists (much of 

 which is kaolin or China clay, and much finely divided 

 carbonate of lime) may then be washed away from a residue 

 of fine sand, which has the same general appearance as 

 the sand of the contorted drift and gravelly boulder beds ; it 

 consists of fragments of minerals of different kinds, including 

 quartz, which occurs as rounded grains, sometimes beautifully 

 smoothed and polished to a gem-like lustre even when only 

 one-fiftieth of an inch in diameter, and of little bits of shells, 

 also rounded and polished. 



The mode of formation of this remarkable boulder clay is by 

 no means easy to discover. The scratched fragments of rocks, 

 some of which have been brought from Antrim, sufficiently 

 indicate the action of ice in some form or other. Ice has 

 carried them and ice has scratched them. The rounded 

 polished sand-grains and shelly fragments probably acquired 

 their characters on a wave and wind-driven beach, from which 

 they were transferred in some unknown way to the boulder 

 clay. The species of well-preserved marine shells concur with 

 the scratched stones in suggesting that the sea in which they 

 lived and in which the boulder clay was deposited was cold. 



The hardness and coherence of the boulder clay is puzzling 

 when we consider that the bulk of it consists of a material 

 which is usually soft and plastic to an extreme degree, but no 

 doubt this character is connected with the presence of cal- 

 careous mud : not less puzzling is the source of the clayey 

 material itself ; it may have been borne along by streams 

 issuing from glaciers, or have been melted out from stranding 

 ice-rafts. 



The sum of our conclusions would thus appear to be that 

 the boulder clay was formed in an icy sea which was tenanted 

 by northern species of molluscs, and that shelly sands from 

 ancient beaches, and ice-borne boulders, brought from far and 

 near, contributed to its formation. 



