440 Proceedings of Royal Society of Edinburgh. [sess. 
the great lime-deposits, consisting solely of lime-incrustations 
formed by the Characea, composed of very conspicuous broken 
stems and leaves. These lime-deposits, in which the percentage 
of lime may amount to 88*50, are dug out of the lakes by 
machinery and used as manure on the fields. 
In other localities within the 30-feet contour a high percentage 
of lime is found, but very often it is impossible to discover from 
what source the lime originates. In our lakes we often find lime- 
incrustations upon other plants besides Characea, especially 
Potamogeton, Elodea, etc. In studying these lime-incrustations 
(1901) I arrived at the following result : — In clear, calm weather 
the lime accumulates in thick flakes on the leaves and stems of 
Potamogeton , etc. ; in stormy weather it is swept off by wave 
action. The precipitation of lime upon the leaves probably goes 
on unceasingly during assimilation ; and the leaves not being able 
to carry the full weight of the lime, broken particles are con- 
tinually dropping off, which sink to the bottom at a greater or less 
distance from the plant. In order to show, as far as practicable, 
that the precipitations of lime from Potamogeton and Elodea play 
a prominent part in the formation of lake-lime, two bottom- 
samples were taken in the Fureso ; one from a bed of Potamogeton 
lucens , the other from a depth of 100 feet, the former containing 
72*41 per cent., the latter 35*30 per cent, of lime. On separately 
weighing the dried leaves of P. lucens and their coatings, it 
appeared that a leaf often carried more lime than its own weight ; 
one leaf weighing 0*35 gram carried no less than 4*1 grams of 
lime. As one plant has often some thirty leaves, it will be easily 
understood that the percentage of lime on the lake-floor beneath 
the dense growths of Potamogeton may be considerably raised by 
means of the constant rain of lime-powder dropping down from 
the leaves. 
Other local formations are the often extensive layers of peat 
arising from the decaying vegetation along the protected shores 
and in the shallow bays, often bordered by abundant growths of 
Phragmites and Scirpus. In the shell-zone lime-deposits likewise 
occur, abounding in mollusc shells ; and in certain lakes these 
shells are transformed into limonite, so that considerable layers of 
“bohnenerz” have been formed; on this point I may refer to 
