184 



Proceedings of the Royal Irish Academy. 



The description of these caves will probably be more intelligible if it is 

 undertaken frora a topographical and not from a chronological point of view. I 

 therefore purpose describing the courses of the streams individually, ignoring 

 the order in which the various explorations were undertaken. 



The mountain of Cuilcagh rises to a height of 2200 feet, and consists of a 

 cap of Yoredale Sandstones resting on a vast plateau of Carboniferous 



430 



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Fig. I. — Streams and Pot-holes of the Marble Arch liistriut. 



Limestone, the stratification of both being, for the most part, practically 

 horizontal. The average height of this limestone plateau is about 650 feet 

 above sea-level ; and it presents an undulating appearance, being broken up into 

 rounded hummocks, which rise to a height of from 100 to 300 feet above the 

 general level. Three streams flow down the northern slope of the mountain, 

 and sink into the limestone at three points about a quarter of a mile apart, to 



