3-1 6 45 



(<7.) — Pre-volcanic alluvial clay and silts, which filled an old 

 Blackwater Valley at a level some hundreds of feet above 

 the present level of the river. 



(b.) — Delta and alluvial deposits laid down in the southern 

 half of a shallow far-spreading lake, formed through a 

 damming of the old Blackwater, by lava-sheets belonging 

 to the Lower series. Erosion by this lake would account 

 for the curious conglomerate at Coagh.* 



(c.) — Sediments and interbedded lignites, whether frag- 

 mentary, non-continuous or formed nearly where grown, 

 synchronizing with the formation of lithomarge, lignite, 

 iron-ore or bauxite upon the surface of the Lower Basalt. 



(d.) — Clays and lignites deposited during and subsequent to 

 the Upper series of outpourings, and the subsequent 

 depression and fracturing. 



(e.) — Glacial deposits and subsequent alluvial accumulations, 

 including fragmentary lignite beds. 



The preservation of such soft materials during the periods of 

 greatest glaciation is a common subject of surprise : I 

 attribute it to the following conditions, viz : — 



First. — That the lake region and south-westward was filled 

 with dead ice, and was shielded by the high ground 

 overlooking Belfast, from the ploughing action of the 

 overwhelming sheet from the north-east, after which — 



Second. — The same region lay upon the axis of a gradually 

 accumulating Irish System, which obstructed an inflow 

 of ice from the north, and subsequently sent its own ice 

 in an overwhelming sheet northward. This sheet of ice 

 carried some pieces of lignite along the Bann valley 



*See previous foot-note (p 638.). It will be borne in mind that the fall in 

 level from Coagh to the margin of Lough Neagh, where the corresponding 

 zone is supp' sed to occur, represented by lignite, is some 200 feet ; which, 

 being due to the post-volcanic depression of the lake area, would not have 

 previously existed. Under these circumstances the dammed waters of the 

 Blackwater could easily have spread westward as far as is supposed. 

 F 



