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 into, 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. 



