448 Proceedings of the Royal Irish Academy. 



The experiments in the laboratory were carried on, more or less 

 simultaneously with the ohservations in the field on peaty streams ; 

 notes on the latter being supplemented by experiments in the former. 



Observations on Peaty Streams. 



These observations were made almost solely on the waters of the 

 Ovoca river basin, and principally on those of its tributaries, the Ow 

 and the Avoubeg. 



The rocks occurring in this basin are granite, clay slate more or 

 less metamorphosed, with a few thin bands of limestone, and patches 

 of eruptive rocks. The superficial coverings to these are the drifts, 

 whether glacial, which may have been transported from some dis- 

 tance, and contain foreign substances ; or meteoric, due to the 

 disintegration of the underlying rocks ; gravels, occurring principally 

 in the valleys; and peat, found on the mountain slopes and in some 

 places in the valleys. 



Prom this it would appear that in this river basin for the most 

 part there is an absence of rocks yielding carbonate of lime, or lime 

 salts ; the sources from which these might be derived being the few 

 fragments of limestone in the glacial drifts, the marls, which are rare, 

 the few bands of limestone scattered through the slates, and the erup- 

 tive ashes containing crystallized calcite. 



Thus the waters of this district may be classified generally as very 

 soft waters, with a few small local exceptions. 



Along the main streams (Ow and Avonbeg), the depth of tint of 

 the colouring varied greatly, from local causes such as the state of 

 a tributary; but in a few cases the variations are, as yet, inexplicable. 

 The most satisfactory results were not, therefore, obtained from these 

 larger streams, but from their tributaries; and of these, one of the 

 most interesting and instructive is the Ballynagappoge brook. 



It had been noticed that, as a rule, in any peaty stream the waters 

 were more darkly coloured at the head waters than anywhere lower 

 down; therefore, when examining the variations in the amount of 

 colouring along the course of a stream, the method usually adopted 

 was as follows: — Starting from the head with a sample of the water, we 

 proceeded down stream, till some alteration in the state of the stream 

 occurred; this might be due to the junction with another stream, or an 

 alteration in the river bed, such as a marked change in the rate of 

 fall, or the occurrence of clay or gravel. Here a second sample of 

 water was taken, and compared with the first, by placing both side by 

 side in two similar tumblers on a white surface, the differences in 

 depth of tint being then noted; proceeding down stream with these two 

 samples, the next comparison was made where the next remarkable 

 change took place; if the depth in tint here was very different from the 

 last, the second sample was discarded, and this third carried down for 

 comparison at the next point of observation, the first, or the sample 



