306 The Realm of Nature CHAP, xv 



Ireland is composed of a vast expanse of the Carboniferous 

 formation, in which the coal-measures are only slightly 

 developed. The mountains are islands of more ancient 

 rock, Silurian and Old Red Sandstone, with metamorphic 

 schist and gneiss, like those of the Highlands, in the 

 north-west. Great masses of volcanic rock occur in the 

 north-east, where the basaltic columns of the Giant's Cause- 

 way form one of the wonders of the world. These harder 

 rocks are prominent on account of their resistance to the 

 erosion which planed down the soft strata into a uniform 

 surface. The centre of Ireland is full of shallow lakes 

 surrounded by peat-bogs, formed by the decay of vegetation 

 in the wet climate on ground too flat to allow of natural 

 drainage. 



REFERENCES 



1 J. Murray, " On the Height of the Land and the Depth of the 

 Ocean," Scot. Geog. Mag. iv. I (1888). 



2 Rohrbach, "Continental Distances." See Scot. Geog. Mag. vii. 

 213 (1891). 



3 J. Murray, "Drainage Areas of the Continents," Scot. Geog. 

 Mag. ii. 548 (1886). 



BOOKS OF REFERENCE 



Longmans' New Atlas. 



J. G. Bartholomew, Macmillan's School Atlas. 



H. R. Mill, Elementary General Geography. Macmillan and Co. 



For explorations in little-known regions see Proceedings of the 

 Royal Geographical Society. 



For papers and references regarding Physical Geography see 

 Scottish Geographical Magazine. 



