Pkthyrrtdge & PiiAEGER — Vegefafioii South of Dublin. 171 



points, where the discharge of water and gravel from the road is 

 considerable, the fringe is continued and expanded as the water 

 continues its way down the valley-side into Glenasmole. Hence it 

 comes about that this slope has a considerable portion of its area 

 covered by larger or smaller patches of this association, which are 

 indicated on the map. 



The two factors which appear to determine the presence of this 

 association on the high grounds are — plenty of water which is not 

 stagnant, but on the move, frequently derived from springs (but 

 brown in colour, and containing humus material) ; and secondly, the 

 presence of a certain amount of gravelly soil derived by the decom- 

 position of the granite, rushes apparently finding any thickness of 

 black peat rather an uncongenial substratum for their roots. 



The presence of an abundance of water, at least on the surface, would 

 not, however, appear to be always a necessity for the presence of 

 considerable masses of Juncus. Thus, on a peculiarly dry spot in the 

 Calluna area, we find the association developed as follows : — 



JuNCUS COMMUNIS. 

 LUZULA MAXIMA. 

 POLYTIIICHUM COMMUNE. 



Sphagnum spp. 

 Rumex Acetosella. 



Galium saxatile. 

 Potentilla Tormentilla. 

 Vaccinium Myrtillus. 

 Calluna vulgaris. 

 Deschampsia flexuosa. 



Again, it must not be supposed that the presence of rushes always 

 indicates the absence of peat. In the Piperstown bog, a small area 

 south of Mountpelier dry gap, at an elevation of 1100 feet, we find 

 the only deposit of peat sufficiently thick to justify the Geological 

 Survey officers in inserting it as such on the recently-published drift 

 survey of Sheet 112 of the one-inch Ordnance map. Here rushes 

 flourish, together with sedges, and the following amongst other 

 species : — 



Eriophorum sjp'p. Potentilla Tormentilla. 



Drosera rotundifolia. Pedicularis sylvatica. 



Potamogeton polygonifolius. \eronica scutellata. 

 Viola palustris. 



The peat cut from this bog for fuel differs considerably in its 

 vegetable composition from that cut, as is usually the case in our area, 

 from a Scirpus bog. 



K. I. A. PROC, VOL. XXV., SEC. B.j 



