of the Fishery Board for Scotland. 281 



other aquatic plants, so that it is difficult to get near the loch in some 

 places. The water of this loch at the time of my visit was clear and 

 pellucid, and thus formed a marked contrast to Loch Balnagowan. Loch 

 Kilcheran was examined only by hand-net from the shore, and some 

 rather rare Ostracoda were obtained, including Erpetocypris robertsoni, 

 Norman and Brady, Darwinella stevensoni, Brady and Robertson, and 

 Scottia broiuniana (Jones). 



Loch Fiart. 



Loch Fiart, which is situated near the south end of the island, is about 

 the same size as the last, and like it has a reedy margin, and can only be 

 fished properly from a boat. The trout in this loch are said to resemble 

 those of Loch Leven, and to attain a similar size. The water of Loch 

 Fiart, like that of Loch Balnagowan, is of a whitish colour, but only during 

 summer. In this case the whitish colour appears to be caused by fine 

 calcareous mud being held in suspension by the water. In winter the 

 water is said to be colourless and transparent. This alternate obscurity 

 and transparency of the water is rather remarkable, but it may be partly 

 or wholly accounted for in this way. The basin of the loch being formed 

 in rock consisting more or less of limestone, a more than usual quantity 

 of calcareous matter in the form of an acid carbonate will be held in 

 solution by the water. During spring-time and summer, when plant life is 

 vigorous, the plants will decompose the carbonic acid, and part of the lime 

 may remain as a fine precipitate suspended in the water. During winter 

 the decaying vegetation may give off carbonic acid, free or combined, 

 in sufficient quantity to redissolve the suspended lime, thus causing the 

 water again to become clear. * Whether this be the true explanation of 

 the phenomona observed or not, the effects described are interesting 

 enough to deserve careful study. 



The following are the lists of organisms obtained and identified in the 

 three lochs referred to : — 



MOLLUSCA. 



Pisidium pusillum, Gmelin. In each loch. 

 Valvata piscinalis, Miiller. Loch Balnagowan. 

 Planorbis albus, Miiller. Loch Balnagowan. 



,, contortus, Linne. Loch Balnagowan. 

 Limncea peregra, Miiller. In each loch. 



* The water of inland lochs usually contains a certain amount of carbonic acid 

 (H 2 C0 3 ) derived from various sources. When the loch is formed in rocks consisting 

 more or less of limestone (CaC0 3 ), the carbonic acid acts on the limestone, forming 

 an acid carbonate of lime, which is soluble and at the same time unstable ; so long- 

 as the water contains excess of carbonic acid it will remain clear and pellucid. The 

 soluble acid carbonate of lime being unstable, very little change in the temperature 

 or otherwise is sufficient to decompose it. For instance, should aquatic vegetation be 

 abundant in the loch, this vegetation, when in vigorous growth during spring and 

 summer, will in the course of its development decompose, in the presence of sun- 

 light, a considerable amount of the carbonic acid which is required to keep the 

 carbonate of lime in solution. (During the summer months, there being very little 

 darkness, this action will be more or less continuous and of course the warmer the 

 weather is the greater the reaction will be. ) On the decomposition taking place, the 

 carbonate of lime is precipitated in the form of a fine white powder, which may 

 remain suspended in the water, imparting to it a milky appearance. The following 

 chemical equations represent the reactions which probably take place — 



H 2 C0 3 + CaC0 3 = CaH 2 (C0 3 ) 2 CaH 8 (C0 8 ) 2 = CaCO ? + H 2 + C + 2 



On the other hand, during autumn and winter the vegetation in the course of its 

 decomposition gives off a certain amount of carbon dioxide, either free or combined, 

 which may form with the water sufficient carbonic acid (H 2 C0 3 ) to redissolve the 

 precipitated carbonate of lime, so that the water will again become transparent. — 

 Andrew Scott. 



