MATURITY 145 



districts in which lochs are common, districts such as the north-western 

 mainland and islands of Scotland, certain narts of Ireland, and almost 

 all the coasts of Norway. It seems reasonable to suppose that the 

 character of each loch, its accessibility from the sea, and its level 

 relatively to sea level, will help largely to influence the movements of 

 the fish which frequent it, so that the deduction of any general principles 

 must necessarily be extremely difficult. There is a broad resemblance, 

 however, between many of our loch basins which is worth adverting to. 

 The most common type of loch with which one is familiar in 

 Scotland is of course the " glen-lake." The origin of these glen-lakes 

 has occasioned much controversy amongst geologists, but it is enough to 

 note here in passing that the once popular theory of excavation by ice 

 action is not generally accepted nowadays. Be that as it may these 

 glen-lakes are of all sizes, ranging from inconsiderable tarns to great 

 inland seas. But their most interest' ns?" feature — so far as regards our 

 immediate subject — is that, owing to an alternate lowering and raising 

 of the general land surface the waters of some of these lochs, within 

 an almost measurable period of time, have become fresh instead of 

 salt. It is possible that the ^-^a has so far encroached upon others as to 

 make their waters salt or brackish instead of fresh. At any rate it is 

 certain that the character of all those that lie near sea-level has changed 

 within recent geological times, and is now in process of gradual change. 

 They are all in different stages of transition. Some of them, in the 

 West of Scotland, lie wholly submerged and open to the sea as in the 

 case of Loch Fyne and Loch Loi g. Others are so nearly at tidal level 

 that the tides flow freely in and out of them through a narrow passage, 

 albeit with much commotion as in the case of the Gareloch, or over a 

 rocky barrier which at low tide cuts off the loch from the sea by a 

 considerable fall, as happens at Loch Etive. Others again, like the 

 Dhu Loch, at Inverary, and some small lochs in the Hebrides — Lochs 

 Stenness and Harray in the Orkneys are of the same character though 



