DEPOSITS OF THE SCOTTISH FRESH- WATER LOCHS 271 
poor in lime, the limestone formations being both rare and exiguous. 
Not only, therefore, is no lime brought into the loch-bottoms as 
detritus, but also the waters are too soft to harbour a flourishing lime- 
secreting fauna, such as might give rise to deposits of biological 
calcium carbonate. Peaty waters, also, may be admitted to have a 
solvent action on lime which tends to prevent its deposition or 
secretion ; but as it is, the Scottish loch and river waters find next to 
no calcareous material upon which to exert their powers. In those 
exceptional regions where limestone formations predominate we may 
expect to find lime on the floors of lochs. A case in point is the 
island of Lismore, from which four calcareous bottom-samples were 
brought, viz. : — 
(1) Loch Baile a' Ghobhainn, 2 feet, CaCOg^Ol per cent. 
(2) „ 88 61 
(3) Loch Fiart, . . . 58 53 
(4) Loch Kilcheran, . 60 40 
The calcareous matter consists of crystalline calcite in small 
fragments, with here and there a piece of snail-shell ; it is, properly 
speaking, a biological precipitate, having been formed by the agency 
of phanerogamous aquatic plants,^ which withdraw carbonic acid from 
the very hard water of these lochs, and cause the deposition of 
calcium carbonate around their stems. Deposits 2-4 are Brown Muds 
mixed with lime. 
Not a single mainland deposit was observed to be calcareous. A 
sample with 75 per cent, of calcium carbonate was taken, oddly enough, 
from Loch Swannay in Orkney, which is not a limestone country. 
The deposit occurs under 8 feet of water at a spot where a patch of 
Potamogeton is reported, and this plant is doubtless responsible for 
its formation. Other bottom-samples from the same loch are quite 
free from lime. 
Scottish Loch and Oceanic Deposits Compared 
The general conditions which govern the formation of loch deposits 
have been indicated to some extent in describing the several classes of 
deposits. It is not uninstructive, in this connection, to compare the 
floor of the lochs with that of the ocean. 
All subaqueous deposits owe their being to three distinct processes, 
viz. : — 
(1) Importation of solid matter from land. 
was exceptionally well sampled, were found to be quite free from calcium 
carbonate. It would have been interesting, in this connection, to know something 
about the content of lime in the loch- water. 
^ West, Proc. Roy. Soc. Edin., vol. xxv. p. 968, 1905. 
