LIMNOLOGICAL PROBLEMS 
395 
in Bodensee 5*4 m. (Amberg, 1904, p. 73 ; see also Geistbeck, 1884-5, 
p. 387). In the high alpine lakes also the transparency may be very 
great, up to 22 m. (Delebecque, 1898a, p. 185); but in the majority 
it is much less. It must, however, be kept in mind that the trans- 
parency has nearly always been measured in summer, when, as a matter 
of fact, it is least. In the Montiggler lakes, Huber (1905, p. 43) has 
shown that the transparency of the water is greater in summer than 
in winter. Rivers coming directly from glaciers carry immense 
quantities of pulverised material into the lakes ; in this case the 
lakes have milky water and are but slightly transparent (Bourcart, 
1906, p. 107). Of the wonderful crystalline ice of the alpine lakes, 
and the very great depths at which the pebbles of the bottom may 
be seen, we have many records (see Geistbeck, 1884-5, p. 368). 
The colour of the water is, as is well known, blue, bluish-green, or 
green ; but the blue lakes, those which have 1-4 in ForeFs scale, are 
rare (Lake of Geneva, d'Annecy, etc.). The majority are green, ForeFs 
scale 5-9 (Lake of Zurich, Vierwaldstiittersee bluish-green ; for the 
rest I may refer to Amberg, 1904, p. 80). Yellowish-brown lakes 
also occur, not rarely with colours exceeding P'orePs No. 9 (Forel, 
Delebecque, Bourcart). 
With regard to the chemical nature it need only be mentioned 
here that Bourcart has clearly shown the close agreement between the 
petrographic nature of the surrounding country and the chemical 
composition of the lake- water (1906, pp. 120-127 ; see also Delebecque, 
1898a, p. 205). Zschokke (1900, p. 38) records that high alpine lakes, 
owing to the lower atmospheric pressure and the slight vegetation, are 
of themselves poor in oxygen, although the mountain brooks supply 
somewhat the want in this regard. The absence of outlets from 
factories and on the whole of detritus of every kind, and thus of all 
oxidisable substances, has the effect, on the other hand, that the loss 
of oxygen during the oxidation processes is slight. 
The organic life of the lakes does not influence the physical and 
chemical qualities of the water in the alpine lakes, nor the filling up of 
the lake-basins, nearly so much as in the Baltic lakes. The plankton 
only exceptionally determines the colour of the water {Oscillatoria)^ 
and has hardly any appreciable effect upon the nature of the bottom, 
as is often the case in the lakes of the Baltic zone (Chitin-, Diatom-, 
Cyanophycea-gytjes), but influences certainly to a considerable 
degree the transparency. In the high alpine lakes the quantity of 
plankton is, as a rule, small ; still, even high alpine lakes may be very 
rich in plankton (Zschokke, 1900, p. 302), but this is then thought to 
be due to abnormal phenomena (afHuents from the St Bernard hospice). 
The steep coasts prevent the occurrence of the broad vegetation 
belts which are so characteristic of the Baltic lakes ; the conditions 
