456 Proceedings of the Royal Irish Academy. 



"Witli a colourless water it yields a clear solution. 



Specimen JV. — A growan, or disintegrating granite, from Augha- 

 vannagh, Co. "\\^icklow. This rock occurs extensively in tliis district, 

 underlying the peat. Deep channels are cut in it by the streams, 

 ■which are not as peaty as might be expected, considering that they, 

 drain extensive bogs. In this growan are large veins of massive quartz 

 and feldspar, which more or less resist disintegration. 



The growan appears composed of quartz, and feldspar (the latter 

 passing into kaolin, or china clay), with black and white mica. 



Insoluble in hydrochloric acid, 86"68 per cent. 



Penic oxide, 3-80 ,, 



Alumina, 6 "24 ,, 



This specimen at first seems to have very little effect on peaty 

 waters, but, after remaining in the water some time, a layer of less 

 darkly- coloured water was observed next to the clay. By repeatedly 

 shaking up the clay and water, at long intervals, a marked reduction 

 of peaty tint was observed in the water. 



Some of the feldspar, mentioned as occurring in large veins through 

 this specimen, after being pulverised, was f oujid to act very similarly ; a 

 reduction of peaty tint only taking place after some time, and after 

 being repeatedly shaken up. This feldspar contains only a very small 

 quantity of iron, is very hard, and little altered. 



In both the above cases, the top of the sediment at the bottom 

 of the peaty water, after standing some time, becomes coated with a 

 brownish substance. 



With respect to the ingredients of these clays that are the active 

 agents in decolourising the peaty water, it was found by experiment 

 that a pure quartzose sand, even when in very large quantities, had no 

 perceptible effect on the colouring of the water. 



Pure gelatinous silica had likewise no effect. 



The portion of a clay that is insoluble in hydrochloric acid was found 

 to have at first no action on peaty water ; but after repeatedly shaking 

 the two up together it was found that the depth of colour was slightly 

 reduced. 



It was also found that freshly precipitated aluminic hydrate, ferric 

 hydrate, and manganese oxy-hydrate precipitated the colouring matter 

 rapidly and efficiently ; of these the alumina is by far the most active : 

 next the iron, the manganese being considerably less efficient. 



The diy oxides of these metals were not found to be nearly so 

 rapid in their action ; in the case of ferric oxide and manganese dioxide 

 it was only after being shaken up repeatedly that any decrease in the 

 tint could be noticed; when left at rest for a considerable time, the 

 layer of water next the oxide became decolourised ; this extended gra- 

 dually upwards, the surface of the oxide being coated with a brownish 

 substance. This clearing of the bottom layer, and its gradual exten- 

 sion upwards, was most marked when a little potassic bisulphate was 



