RAMBLES OF A GEOLOGIST. 449 



from where the lower loch opens to the sea, of only marine 

 plants, then of marine plants mixed with those of fresh- water 

 growth, and then, in the upper sheet of water, of lacustrine 

 plants exclusively. And the fauna of the loch, like its flora, 

 is, I was led to understand, of the same mixed character; 

 the marine and fresh-water animals having each their own 

 reaches, with certain debateable tracts between, in which each 

 expatiates with more or less freedom, according to its nature 

 and constitution, some of the sea-fishes advancing far on the 

 fresh water, and others, among the proper denizens of the 

 lake, encroaching far on the salt. The common fresh-water 

 eel strikes out, I was told, farthest into the sea-water; in 

 which, indeed, reversing the habits of the salmon, it is known 

 in various places to deposit its spawn : it seeks, too, impa- 

 tient of a low temperature, to escape from the cold of winter, 

 by taking refuge in water brackish enough in a climate such 

 as ours to resist the influence of frost. Of the marine fishes, 

 on the other hand, I found that the flounder got greatly higher 

 than any of the others, inhabiting reaches of the lake almost 

 entirely fresh. A memoir on the Loch of Stennis and its pro- 

 ductions, animal and vegetable, such as a Gilbert White of 

 Selborne could produce, would be at once a very valuable and 

 very curious document. By dividing it into reaches, in which 

 the average saltness of the water was carefully ascertained, and 

 its productions noted, with the various modifications which 

 these underwent as they receded upwards or downwards from 

 their proper habitat towards the line at which they could no 

 longer exist, much information might be acquired, of a kind 

 important to the naturalist, and not without its use to the 

 geological student. I have had an opportunity elsewhere of 

 observing a curious change which fresh-water induces on the 

 flounder. In the brackish water of an estuary it becomes, 

 without diminishing in general size, thicker and more fleshy 

 than when in its legitimate habitat the sea ; but the flesh 



