138 



The Irish Naturalist. 



December, 



of the fact that all the material encountered in the field 

 was glacial drift which had been converted by degrees into 

 sand and gravel, whether the sand and gravel occurred as 

 the low undulating hills of the Curragh of Kildare or as 

 the narrow sinuous mounds of the Esker Riada type. 



As our knowledge of the glacial deposits of Ireland 

 became more accurate the submergence theories connected 

 with the Ice Age became untenable and the high-pitched 

 gravel mounds of the Esker Riada type came to be regarded 

 as casts of the subglacial or englacial tunnels which, had 

 been excavated in the ice sheet by percolating water. This 

 theory which is usually connected with the name of Dr. 

 Hummel, the Swedish geologist, who has made a special 

 study of Eskers or Osar in Sweden, has been regarded with 

 favour, both in Europe and America, as affording a satis- 

 factory solution of the problem. In recent years an 

 important modification of Hummel's theory was proposed 

 by De Geer, who, while retaining the subglacial or englacial 

 tunnel for the supply of the necessary water-worn material, 

 considered that the stream issuing from the glacier should 

 deposit its load under water in a lake or stretch of stationary 

 water existing along the front of the ice sheet. 



The possible or probable existence of these lakes or 

 stretches of water in Ireland in late glacial times has 

 been the subject of much discussion among Irish geologists, 

 and various proposals for a lake in the central plain has 

 been brought forward, whether as consequent on differential 

 movement of the land at the close of the Ice Age or as the 

 result of possible ice barriers closing the outlets of the 

 central depression. No definite decision had been arrived 

 at when Prof. Gregory in the paper under review proposed 

 a return to a postglacial submergence, in order to obtain 

 the necessary sheet of water required by De Geer's theory, 

 evidence for which he considered to exist in the presence 

 of the shelly deposits which occur in various localities and 

 at various elevations in Ireland. 



The proposal put forward by Prof. Gregory of a post- 

 glacial submergence of the central plain of Ireland in order 

 to explain the origin of the Eskers must be regarded as 

 revolutionary, and one which could only be accepted by 

 Irish geologists after very deliberate consideration. Its 



