516 THE FEESH-WATER LOCHS OF SCOTLAND 
In areas which have relatively recently been raised above the sea, 
Genetic and in areas which have recently been covered with an ice-cap, the 
relationship, j.-^^^. gygtems are young or adolescent, and lakes are numerous. 
Through the action of the ordinary agencies of disintegration and 
denudation lakes continually tend to disappear, their outlets being 
cut down, and their basins being filled up with detrital matter and 
organic OTOwths. Hence in mature river basins there are relatively 
few lakes, unless the river system has been rejuvenated by mountain 
growth. ^ 
o 
base with an inorganic acid ; that is, the word " salt " comprises such compounds 
as calcium carbonate, sodium sulphate, magnesium chloride, etc., whilst sodium 
chloride will be referred to as such or as " common salt." Similarly, the words 
"saline " and "salinity" are to be understood as applying to total dissolved solids 
and not to an individual salt, whether sodium chloride or any other. As regards 
the term " alkaline," it will suffice for present purposes to define alkaline waters 
as those which hold an excess of sodium carbonate (with more or less potassium 
carbonate) in solution. 
1 This genetic history of lakes and river basins is well outlined by Professor 
Davis in the following extracts {Science, vol. x. pp. 142-143, 1887) : — 
" When a new land rises from below the sea, or when an old land is seized 
by active mountain-growth, new rivers establish themselves upon the surface in 
accordance with the slopes presented, and at once set to work at their long task 
of carrying away all of the mass that stands above sea-level. At first, before the 
water-ways are well cut, the drainage is commonly imperfect : lakes stand in the 
undrained depressions. Such lakes are the manifest signs of immaturity in the 
life of their drainage system. We see examples of them on new land in Southern 
Florida ; and on a region lately and actively disturbed in Southern Idaho, among 
the blocks of faulted country described by Russell. But as time passes, the 
streams fill up the basins and cut down the barriers, and the lakes disappear. A 
mature river of uninterrupted development has no such immature features 
remaining. The life of most rivers is, however, so long, that few, if any, com- 
plete their original tasks undisturbed. Later mountain-growth may repeatedly 
obstruct their flow ; lakes appear again, and the river is rejuvenated. Lake 
Lucerne is thus, as Heim has shown, a sign of local rejuvenation in the generally 
mature Reuss. The head waters of the Missouri have lately advanced from such 
rejuvenation ; visitors to the National Park may see that the Yellowstone has 
just regained its former steady flow by cutting down a gate through the mountains 
above Livingston, and so draining the lake that not long ago stood for a time in 
Paradise Valley. The absence of lakes in the Alleghany Mountains, that was a 
matter of surprise to Lyell, does not indicate any peculiarity in the growth of 
the mountains, but only that they and their drainage system are very old. 
" The disappearance of original and mountain-made lakes is therefore a sign 
of advancing development in a river. Conversely, the formation of small shallow 
lakes of quite another character marks adolescence and middle life. During 
adolescence, when the head-water streams are increasing in number and size, and 
making rapid conquest of land -waste, the lower trunk-stream may be overloaded 
with silt, and build up its flood -plain so fast that its smaller tributaries cannot 
keep pace with it : so the lakes are formed on either side of the Red River of 
Louisiana, arranged like leaves on a stem ; the lower Danube seems to present 
a similar case. The flood-plains of well-matured streams have so gentle a slope 
