968 Proceedings of Royal Society of Edinburgh. [sess. 
the growth of the higher plants in the shallow water, where its 
influence is felt. Unless sheltered by adjacent hills, all the lakes 
will he almost or quite devoid of vegetation on their eastern shores ; 
whilst the western shores and hays, sheltered from the prevailing 
wind, will have an abundance of vegetation (figs. 47, 48). We do 
find, however, even in exposed parts of the lakes, large rocks often 
covered with mosses, hepatics, algae, etc. By reason of the pre- 
serving action of humic acids, the organic remains about the 
lakes do not readily decay, but undergo a slow process of dis- 
integration and form a sort of liquid peat. Owing to this action, 
suitably situated shallow places about peaty lakes become reclaimed 
by the growth of plants quicker than in waters free of humic 
acids. 
2. The Lismore Area. — Here we find conditions absolutely 
different from those existing in the Loch Hess area. There is no 
moorland peat formation at Lismore that can possibly drain into 
the lakes. The geological formation throughout the island is 
limestone. The land is almost entirely in a more or less culti- 
vated state, and supports a large number of sheep and cattle. 
Instead of humic acids an appreciable supply of ammonia salts 
will therefore find access to the lakes. The three lakes on 
Lismore are hut slightly elevated above sea level, and are 
sheltered from wind by adjacent low hills (figs. 108, 109). A 
marked difference from the Hess area is, that the waters of the 
lakes are heavily charged with calcium carbonate. In contra- 
distinction to the lakes of the Hess area, the water of these lakes 
is pellucid. It is so clear that one may look over the side of a 
boat and see the bottom through twenty-five feet of water. In 
consequence of this clearness, the photic zone of vegetation is much 
less restricted than in the Hess area. The rocks and stones are 
covered with an incrustation of lime which gives them a peculiar 
sponge-like appearance (fig. 1). The rounded, water- worn, and 
polished stones found on the shores of the Hess district are not 
to he seen at Lismore (fig. 2). The lakes being sheltered from 
the wind by hills, their shores are not subjected to frequent and 
powerful erosion by the waves ; they are consequently more or less 
surrounded with a littoral vegetation. Many of the plants in 
these lakes are heavily coated with an incrustation of calcium 
