of the Fishery Board for Scotland. 
281 
otlior 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, incduding Erpetocypris rohertsoni, 
Norman and Brady, DarivineUa stevensoni, Brady and Robertson, and 
Scottia browniana (Jones). 
Loch Fiart. 
Loch Fiart, which is situated near the south end of the island, is about 
tbe 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 coloui' appears to be caused by fine 
calcareous mud being held in suspension by the water. In M^inter 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 j^usilhwi, Gnielin. lu each loch. 
Valvata piscinalis, Miiller. Loch Balnagowan. 
Planorhis albus, Miiller. Loch Bahiagowan. 
contortus, Liniie. Loch Balnagowan. 
Limncea peregra, Miiller. In each loch. 
* The water of inland lochs usually contains a certain amount of carhonic acid 
(HaCO;^) derived from vaiious sources. When the loch is formed in rocks consisting 
more or less of limestone (CaCOg), 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 m- ill 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 })lace — 
H.COg + OaCOa CaH2( 003)2 CaH2(C03)2 = CaCOg + HgO + C + Og 
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 (H2CO3) to redissolve the 
precipitated carbonate of lime, so that the water will again become transparent. — 
Andrew Scott. 
