Proceedings of the IJelfast Natural History and Philosophical Society 1919-1920 (1). 



11th Novemher, 1919. 



Councillor Henry Riddell, M.E., M.I.M.E., in the Chaii 



THE NORTH OF IRELAND DURING THE 



GLACIAL PERIOD. 



By Arthur R. Dwerryhouse, D.Sc, M.R.I.A., F.G.S. 



Lecturer in Geology, Queens University, Belfast. 



(Abstract). 



The subject was introduced by a description of the traces 

 left by the passage of ice-sheets over a country. 



The scratches and grooves impressed upon rock surfaces 

 were illustrated and their importance as records of the direction 

 of movement was discussed. 



The deposits formed by glaciers next received attention^ 

 and these were divided into (a) Boulder Clay, an unstratified 

 clay with striated stones, many foreign to the district in which 

 they now rest ; and (6) stratified clays, sands and gravels 

 accumulated by the action of the running water associated with 

 ice. The Boulder Clay occurs either in sheets of irregular 

 thickness or in slightly elongated ridges with smooth contours, 

 such as those which are so common in County Down, and known 

 as drumlins. The stratified clays are lake deposits formed in 

 standing water near the ice-margin, and the sands and gravels 

 consist of coarse materials, lying in sheets or fans, accumulated 

 under somewhat similar conditions, or in long tortuous ridges, 

 called Eskers, the product of streams of water flowing in tunnels 

 in or beneath the ice. 



Accumulations of clay, stones and sand which are formed 

 along the margins of an ice lobe, are known as moraines and 

 serve to indicate the limits of the ice at its maximum extension 

 and at various stages of its retreat. 



The stones which are carried by the ice for long distances 

 from the parent rock are called Erratics, and serve to indicate 



