144 



The Irish Naturalist. Ju^^' 



foraminifera would be likely to escape the shearing stresses in 

 the ice during this process more readily than the larger 

 organisms," And so that bug-bear, the " Irish Sea glacier," 

 stalks unabashed through the Memoir, and a sketch-map on 

 p. 52 shows clearly how its edge struck the Down shore of 

 Belfast Lough, and poured across the Silurian uplands into the 

 Strangford basin. 



The portions of the Memoir which, to our mind, furnish the 

 most suggestive reading, are those which deal with the Belfast 

 basin. Here we find an interesting fact put forward, and also 

 an interesting theory. The fact in question is that the Pre- 

 glacial course of the River Lagan differed considerably from 

 its Post-glacial course, the choking of the valley with drift 

 having pushed the stream far to the eastward of its former 

 bed ; while the theory referred to is the existence of an ex- 

 tensive late-Glacial "Lake Belfast" in the valley in which 

 now the city stands. As regards the former point, the section 

 across Belfast, illustrated on p. 85, and the remarks on 

 the subject on p. 64 and elsewhere, can be referred to With 

 regard to " Lake Belfast," we have here a most interesting 

 suggestion, and it is much to be regretted that the steady 

 labour of mapping over 200 square miles of country left the 

 Surve}^ officers no time for the working-out of the problem. 

 The occurrence of such lakes along the margin of an ice-sheet 

 is a w^ell-known phenomenon''. In the present instance, the 

 prevalence of gravelly deposits contouring the Lagan basin, 

 and fringing the well-known red sands of the Belfast suburbs, 

 is considered indicative of lake conditions. These gravels 

 extend along the foot of the hills between Holywood and 

 Knock, are much pronounced at the entrance of the Dun- 

 donald valley, and continue up the edges of the Lagan valley. 

 The presence of such a lake, dammed in by an ice-^obe of 

 the Irish Sea glacier extending up Belfast Lough as far as 

 Holywood, would easily account for the formation of those 

 striking deposits of fine red sands (appropriately named 

 " Malone Sands " in the Memoir), which have arrested the 

 attention and puzzled the mind of every worker in the Belfast 

 district. It is true that the disposal of these sand-banks does 



■• For an account of a similar Glacial lake in the Dublin area, see W. B. 

 Wright : " The Glacial origin of Gleudoo." — I,N., xi., 96-102. 1902, 



