450 Proceedings of the Royal Irish Academy. 



The head waters above Ballynagappoge bridge are deeply tinted 

 ■^ith peaty colouring matter ; the bed of the stream here is marshy, 

 with a slaty rock appearing in places ; below the bridge there is more 

 rock, less marsh, while a little gravelly clay appears in places ; some 

 distance down, the stream is joined by another of about equal size and 

 about equally coloured, but which has been flowing along a somewhat 

 gravelly bed. Just before its junction with this stream the brook had 

 not so deep a colour as it had at Ballynagappoge bridge. The united 

 streams wash against the foot of a blue clayey cliff, from which a con- 

 siderable quantity of clay is evidently removed during flood time ; 

 below this cliff the bed of the stream is composed of a bare slaty rock 

 with very little gravel resting upon it ; the depth of tint of the water 

 gradually but very slowly becomes reduced along this part of the course. 

 Here the stream flows rapidly and forms a succession of little falls; 

 this rocky bed, with its rapid fall, giving place at about 500 yards 

 above Eosahane bridge to a clayey and gravelly bed with a reduced 

 rate of fall. Between the point where this change occurs and the 

 bridge the peaty colouring in the stream, which was considerable, is 

 reduced to a mere trace, while a short distance below the bridge it is 

 completely removed. Along this portion of the stream, just above the 

 bridge, where the fall is slight, there are several marshy places 

 from which iron-stained waters flow into the brook ; this staining is 

 due to the waters containing some ferrous salt (probably ferrous car- 

 bonate) in solution, which, on contact with the air, is decomposed or 

 oxidized, depositing ferric hydrate or ochre. On the stones and in the 

 pools about this part of the stream there is a dark brownish deposit ; 

 some of this was collected with the surrounding water, which had a slight 

 peaty tinge. On standing, this water gave a yellow ferruginous pre- 

 cipitate, the water becoming most beautifully clear and limpid. It 

 was found that the sediment collected consisted of a little sand and 

 clay, with iron, alumina, magnesia, a little manganese and organic 

 matter. 



These iron springs appear to be the agents that, to a great extent, 

 clear the waters ; for although in all probability, clays in suspension, 

 or the very small quantity of soluble matter that is dissolved out of 

 them, will carry down a large amount of peaty colouring matter, yet, 

 except when present in very large proportion, they seem incapable of 

 decolourizing the waters completely. 



The ferrous salts in these waters are probably derived from the 

 reduction, by decomposing organic matter, of the ferric salts contained 

 in the underlying rocks and clays. 



The decolourizing of the waters of this brook is evidently not due 

 to the direct oxidation of the peaty matter ; nor is the diminution of 

 the depth of tint due to dilution. In this stream it so happens that, 

 where the fall is greatest, there the clearing of the water is least. 



During December, 1880, it was remarked that the main rivers con- 

 tained very little peaty colouring matter in them ; about this time there 

 had been slight frosts in the valleys, but upon the mountains there was 



