104 [Proc. B.N.F.C., 



all the way to the north coast, most of which have been since silted 

 up by the washings of the land, their sites being now occupied by 

 peat bogs. Shallow lakes may be expected to occur in any district 

 from which the sea has retreated, especially if the land had previous 

 to subsidence been subjected to the scooping out power of glacial 

 ice. Such lakes would be at first salt, but this would soon be 

 carried off by the discharging river. There is unmistakable evi- 

 dence that this district was covered by the sea for a long period 

 after the deposition of the boulder clay. This deposit has been 

 almost entirely swept away from all the lower lands, its place being 

 occupied by water-rolled pebbles and accumulations of mud, sand, 

 and gravel. Farmers are often puzzled by this circumstance. 

 They wonder why it is that the heavy clay lands are confined to 

 the hills, while the sandy and gravelly soils occur at lower levels. 

 The explanation is, that the sea swept away the boulder clay, ex- 

 cept an occasional patch of a tenacious character, which resisted 

 its denuding power. Such patches would appear as islands, while 

 the lower ground would be covered with the sorted and water- 

 rolled materials which the sea had spread along its bottom. Simi- 

 lar occurrences have taken place in Down. There is good ground 

 for believing that since the Glacial period Belfast Lough and 

 Strangford Lough were connected along the valley through which 

 the County Down railway runs. This valley is well seen from the 

 top of the Cave hill. Here, as well as in Antrim, the tenacious 

 unstratified clays are mainly confined to the higher ground, the 

 subsoil of the lower lands consisting of stratified deposits of mud, 

 sand, and gravel. 



There are certain low hills or ridges, called "Eskers," found 

 abundantly at low levels in all parts of the country, the origin of 

 which has not been satisfactorily explained. Good specimens may- 

 be seen along the line of the Northern Counties railway, also be 

 tween Dundonald and Comber. They are also very numerous in 

 County Tyrone, particularly between Omagh and Dungannon. 

 They are composed of sand and gravel, usually in regular layers. 

 Now it is plain that such accumulations of stratified materials must 



