Stewart— Mollusca of the Boulder Clay. 
167 
made, as in quarries or roads, they discover the Boulder Clay equally on the 
hill-side or level plain. 
The Glacial Drift has been divided by geologists of eminence inth three 
stages First, the lower Boulder Clay, the most extensive, and displaying the 
greatest evidence of Arctic conditions ; second, certain sands and gravels 
deposited under milder conditions of climate ; and third, the upper Boulder 
Clay, which is said to indicate a recurrence of Arctic conditions. My researches 
do not lead me to accept this classification. I am unable to separate it into 
upper and lower, and the gravels said to be interglacial seem to be only local 
modifications of the deposits of one continuous period, during which Arctic, or 
semi- Arctic, conditions prevailed over this country without any interval of 
relaxation. The sands and gravels at Ballyrudder, near Glenarm, which 
Professor Hull regards as interglacial,* yield abundant specimens of a fauna as 
Arctic in character as any portion of the Boulder Clay, and are overlaid by an 
unstratified clay which I cannot distinguish from deposits which are said to be 
lower Boulder Clay. 
FOSSIL LOCALITIES. 
BELFAST WATERWORKS. 
The Boulder Clay at this locality has yielded a much larger number of 
Molluscan remains than any other similar deposit in Ireland. Forty-seven 
different shells are enumerated in the subjoined list, mostly collected in 1842-3 
by the late Messrs. James Bryce, F.G.S., and George C. Hyndman, who pub- 
lished their results in Portlock’s Report on the Geology of Londonderry, 
PP- 738 - 9 - A further and more complete list of the shells of the Waterworks 
was given by Mr. Bryce in the “Philosophical Magazine,” vol. 26, pp. 433-5. 
This deposit of Boulder Clay was proved to be undoubtedly rich in fossils ; but 
it is not, however, to be inferred that, as compared with other localities, this 
spot was so excessively rich as would appear from the lists. Mr. Bryce states 
that about ten thousand cubic yards of the clay were removed during the exca- 
vations for the lower reservoir, and that the great number of shells obtained was 
due to the watchfulness of various collectors. In other instances only the 
surface of a limited section can be examined, and it will be seen that no fair 
* Hull— Physical Geology and Geography of Ireland, p. 88. 
