Vol. 65.] THE CARBONIFEROUS LIMESTONE OF COUNTY CLARE. 547 



Turning again to the eastern edge of the plateau, the main escarp- 

 ment can be followed southwards, from Slieve Carran and Eagle's 

 Rock, a magnificent vertical cliff 500 feet high, past the remarkable 

 valleys of Glencolumbkille and Glenquin, to the north-west of 

 Inchiquin Lough, near Corrofm. The successive terraces which 

 build up these escarpments are well shown in the hills east 

 of Glencolumbkille. The beds to the immediate south of this 

 neighbourhood undulate considerably to the north-west and south- 

 east, being well exposed on the outlying hill of Mullagh More. 



The major features of this extensive plateau are repeated on a 

 smaller scale over the whole of its surface, and many remarkable 

 examples may be observed of more or less circular depressions and 

 deep valleys surrounded on every side by steep terraced rock-faces. 

 No wilder or more desolate spot can be found in the British Isles, and 

 well does it deserve the name of Burren (borr = great, onn = a 

 stone or rock). 



From the eastern escarpment to the border of the county stretches 

 a broad limestone plain covered by numerous lakes. This low ground 

 never rises above 200 feet, and has a mean altitude of 100 feet. 



The southern district presents a totally different aspect. The 

 limestone no longer forms a prominent topographical feature, but 

 occupies all the low-lying ground in the centre of the county ; while 

 the high ground is formed, on the west by Coal Measures, and on 

 the east by Old Red Sandstone and Silurian rocks. These older 

 formations appear in two large anticlinal flexures with a north- 

 easterly trend, forming the mountains of Slieve Aughty and 

 Slieve Bernagh, between which lies a broad syncline of Car- 

 boniferous Limestone. The outer margin of this syncline is formed 

 by Lower Limestone and Shales (Tournaisian), the successive zones 

 of which can be traced continuously round its outcrop, while the 

 Visean or Upper Limestones occupy the core. All these beds are 

 more or less strongly folded, the dips, though varied by minor 

 flexures, as a rule following the general trend of the syncline. 



The structure of the country, which is thus comparatively simple, 

 is, however, greatly obscured by a covering of Drift, chiefly composed 

 of limestone-debris from the underlying rocks. This central lime- 

 stone area has a mean altitude of 150 feet, but reaches sea-level 

 along the estuary of the Shannon. It rises to 300 feet in the 

 neighbourhood of Tulla, and also to the west of Ennis, where it 

 forms conspicuous rocky crags beneath the abrupt Coal-Measure 

 escarpments. The drainage is effected, to the south by means of the 

 Fergus and Owengarney Rivers and their tributaries, which flow 

 into the Shannon ; and to the east by the Graney River and other 

 minor streams flowing into Lough Derg. 



Lower Limestone beds are again met with, on the south-eastern 

 slopes of the Slieve Bernagh Mountains, in the district north of 

 Limerick. 



