TOPOGRAPHY AND GEOLOGY. 9 



Mountains and Donegal Bay. The scenery partakes, 

 The- Central Plain, in consequence, of the underlying geological mono- 

 tony ; the features of the cramped southern synchnals 

 are here spread out over the half of Ireland (Fig. 6). 



Yet the landscape is soft and pleasing, tender in its tints of green and 



brown ; here and there the view is bounded by far blue hills, which lie 



always on the horizon, and which retain the same distant air throughout the 



journey of a summer day. Long ridges and heaps of gravel, the familiar 



'■' green hills," are the only elevations near at hand. The great cumulus 



clouds that throw their shadow^s across the plain seem an essential portion 



of the landscape ; the heavens and the earth here meet in a unity unknown 



amongst the sterner mountains. The sun shines out upon the white waters 



of a lake, fringed, perhaps, with a belt of larches or Scotch firs. The edge 



of the lake seems quite an accidental boundary, and the stones, when the 



water sinks sufficiently low, are seen to be excavated 



Lough Corrib. by solution into fantastic forms along the shores. 



Lough Corrib itself, with its low and flat-topped 



islands, is only a watery region of the plain. The eastern part of Lough 



JNIask belongs, similarly, to the limestone area, while the ancient Silurian 



rocks rise in sudden dignity on its western shore. 



Clew Bay. Clew Bay, dotted with islets, is merely another lake of 



the Carboniferous Limestone region, into which the 



sea has become admitted in comparatively recent times. 



The great and shallow synclinal which thus provides such uniformity of 

 feature is split into two on the north-east by the old Caledonian axis of 

 Ne\\"ry, which runs in reality from Co. Longford to the coast near Strangford 

 Lough. Hence, in this region, a tumbled and rougher country intervenes 

 between the grazing-grounds of Meath and the lowlands of Lough Erne. 

 The road from Dublin to Belturbet provides a characteristic traverse of the 

 old floor of Ireland, which here again rises to the light of day, the watershed 

 occurring in an almost highland landscape at Cross Keys. 



The Shannon, after its first rapid drop from Cuilcagh, a scarp of Upper 

 Carboniferous Sandstone in Fermanagh, becomes 

 »,, „, essentially a river of the plain. It wanders south 



e b annon. through the broad limestone country, in an indepen- 

 dent and unbounded fashion, now and again expand- 

 ing into lakes, which are enlarged by the actual solution of their shores. 

 At the south end of Lough Derg, it cuts across the local anticlines, amid 

 mountain-scenery at Killaloe ; but it then winds again over ledges of lime- 

 stone to Castleconnell and the Atlantic. The Erne is a river of the same 

 class, in which the lake-feature has become predominant. Lough Oughter, 

 with its abundant islands, is really only a network of branches of the stream. 

 Upper Lough Erne is little more ; the wanderings of the river, in materials 

 so easily removed, have here made it assume the aspect of a lake, the islets 

 remaining as relics of its former banks. Lower Lough Erne possesses 

 bolder features ; but here we are in an area of more complex geological 

 structure. On the south-west, bold masses of Carboniferous sandstone, 

 and even the Coal Measure cappings of Arigna and 

 Ari^na Coal-field ^o^S^ Allen, have escaped the general denudation. 

 ° ' * The out-liers of coal-bearing strata on these hills are 



a melancholy reminder of the amount that has been 

 washed away from the great plain to southward. The Carboniferous Lime- 

 stone also has here been lifted into prominence, and inland cliffs and scarps 



