144 THE VALLEYS OF SOME OF THE IRISH LAKES. 



" that these holes are caused by the acid generated 

 from the decay of mosses or lichens, humic acid 

 being formed from the decay of the vegetable 

 matter that might grow in or be swept into the 

 small hollows in the stone, and carbonic acid from 

 the final decay, the latter acid saturating the water, 

 which would then act on the limestone. Once the 

 hollow is begun, all acid in the water remaining on 

 the stones, along with what may form from the decay 

 of any vegetable matter that may be swept into them, 

 will be concentrated as the water evaporates ; there- 

 fore principally act on the bottom of the hollow, and 

 thereby bore the cylinders through the blocks." 



In this way the holes which are like inverted funnels 

 might also be explained, for as such holes deepened, 

 the water could not, in them, evaporate as quickly as 

 when they were shallow ; therefore the contained 

 acid would act on the sides as well as on the bottom 

 of the holes, and thereby enlarge as well as deepen 

 them. If the acid generated from the plants is the 

 cause for these weatherings, the reason for their being 

 only found in the vicinity of lakes may be accounted 

 for by supposing that the moisture from the lakes 

 helps the growth of the acid-forming vegetables. 



Against these suggestions it should be mentioned 

 that in one locality, Dringeen Oughter, on the shores 

 of Lough Mask, a cup weathering occurs, not on the 

 surface of the rocks, but on the surface of one of the 



