THE LAKE-BASINS OF IARCONNAUGHT. 109 



them, pounding up the water, and thereby giving rise 

 to a small lake. When a loughaun is situated on 

 low ground, there usually is a swamp or morass con- 

 nected with it ; but if on high ground, or on a water- 

 shed, as is not uncommon, its margin is well defined, 

 and generally higher than the surrounding bog. This 

 high, prominent margin seems due to the spring- 

 water equalising the temperature during the different 

 seasons of the year ; therefore, in the frosts of winter 

 and the extreme heat of summer, when vegetation is 

 stopped on the rest of the bog, here it is in full 

 vigour. Usually the springs are perennial, and the 

 sides of the ponds are perpendicular, or may even 

 cove in; some, however, are only full in winter or 

 wet weather, consequently in summer the bog at the 

 sides weathers and falls in, making the loughaun 

 more of the nature of a boggy pool. The drainage 

 from a loughaun is nearly always by soakage through 

 the surrounding peat ; sometimes, however, it must 

 be subterranean, probably between the peat and the 

 underlying strata, while in a few cases a crack has 

 opened during a dry summer in the surrounding bog, 

 and been kept open by the stream from the loughaun 

 flowing through it. From the above description, it 

 is evident that bog-basins are not due to denudation, 

 but to a growth of vegetable matter, while indirectly 

 they are caused by a break or fault in the subjacent 

 rocks from which the spring issues. 



