84 



rocks are limestone. Similar carvings are said to 

 be done by the sea, but we have never seen any 

 examples of the kind, and it would appear necessary, 

 in order to accomplish it, that the sea should be 

 tideless. 



If mushroom-rocks have been formed by the aid of 

 the water of a lake or a sea, they will be found on cer- 

 tain horizons, which is not the case when they are due 

 to meteoric action. On the hills of Devon and Corn- 

 wall, England, and the crags of Sligo, Mayo, Galway, 

 and other places in Ireland, they are numerous, and 

 it may be seen that, in general, the side open to the 

 prevailing wind is more rapidly weathered than the 

 others. Wind action may also scoop out a soft bed 

 in a cliff, undermining the upper beds. On the 

 Forum amore mountains, south of the Erriff river 

 valley, Co. Mayo, there are, in places, outliers of car- 

 boniferous rocks, and in them are subordinate beds 

 of friable sandstone. The latter, when exposed to the 

 south-west, from whence come the most prevalent 

 winds, are rapidly denuded, the wind driving the 

 rain into them, to disintegrate them, and afterwards 

 blowing them away piecemeal, thus undermining 

 large masses of rock which eventually topple over 

 and form a rocky detritus. 



The moist climate of West Galway diminishes, by 

 nearly one half, the amount of work the wind can do 

 in this way ; as, during wet seasons, deposits of blow 



