202 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Jan. 22, 



On the surface are marks of glaciation, which wore the rock and 

 shaped the surface, and carried the debris southwards to "Waterford, 

 along a wide hollow which goes from one end of Ireland to the 

 other, along the courses of the Ban and the Waterford rivers. 



At the edge of the country are marks of horizontal undermining 

 at " the destructive plane of the sea." 



The marks of rivers and weather are also plainly seen (but they 

 are insignificant about Lough Neagh) in plains and highlands. The 

 amount of weathering is measured on quartz-veins, which retain 

 glacial marks and stand out a couple of inches at most from the 

 weathered surfaces. Rivers work only in their narrow beds ; and 

 most of them still flow on drift in low grounds. Since ice vanished 

 and the land rose, these last-named engines have done little work. 



VII. Limestone. — I will take another case in which the main 

 hollow trends N.W. 



The Sligo hills to the south of Donegal Bay are steeply scarped 

 plateaux with cliffs and talus. The outline is often like that of the 

 Antrim coast ; the plan is like that of the Antrim glens. The chief 

 difference in the forms of these two sets of hills is in the greater 

 steepness of harder slopes in Sligo. Ridges end in sharp peaks like 

 needles off the Atlantic coasts. 



The tops of these hills and their high plateaux are made of flat 

 beds of blue Mountain-Limestone, resting conformably upon grits 

 and sandstones. 



Cliffs are fractures ; and some of these may coincide with faults. 

 If so, I could not find them. 



These beds were deposited horizontally at the bottom of a sea, 

 long before the Antrim chalk. Elsewhere they have been greatly 

 disturbed and bent into basins, notably about Lough JNeagh, in the 

 coal-field near Dungannon. Their geology is studied because of the 

 coals which accompany Mountain-Limestone in Ireland and else- 

 where. But about Beinn Gulban, famous in Celtic tradition, the 

 beds are flat or slightly inclined. Like Antrim chaBi, their edges 

 appear on the sides of hills, in deep glens, at points, in " cols," and 

 in cliffs. It is manifest on the ground that these Sligo glens have 

 been hollowed out of a raised plateau, and that more than 2000 feet 

 of limestone and lower beds have been carried away from large areas 

 in this region about Lough Erne and Donegal Bay. Not one sample 

 of Mountain-Limestone could I find in drift about Dangloe and the 

 northern end of Ireland ; but the low lands of Central Ireland are 

 thickly covered with limestone-gravels. At Galway are sections of 

 Boulder-clay full of scratched polished fragments of limestone ; and 

 great blocks of it have been carried on to hills about Kenmare, in 

 Kerry, in the south-west. Like the flints, the limestone-drift tra- 

 velled southwards. Measuring from the limestone in Sligo to the 

 plain, about 2000 feet of rocks have been removed. The fragments 

 did not go far north ; but a great stream of ice certainly travelled 

 from Lough Erne north-westwards into Donegal Bay. The marks 

 are well preserved at BaHy-Shannon on sandstone. 



The Irish coal-fields now are patches scattered about the country, 



