DEPOSITS OF THE SCOTTISH FRESH-WATER LOCHS 265 
(a) derived from a mixture of Brown Muds, and another (b) from a 
Loch Lurgain mud, 146 feet, were examined quantitatively, after 
drying at 110° C. They contained : — 
On total substance^ iron as Fe^O^ . 
• 1 . 1 f Carbon 
On non-mmeral portion only < rr ^ 
^ ( Hydrogen 
(a) 
7*9 per cent. 
51-8 
5-0 
(^) 
6"1 per cent. 
53-4 
4-6 
Alkali-humus is not free from nitrogen, but to determine in what 
form and amount this element is present more material would be 
needed than was at disposal. The organic matter not dissolved by 
alkali is a light yellowish-grey, not markedly ferruginous powder, 
which evidently consists of disaggregated but not fully decomposed 
vegetable tissue ; under the microscope it appears as a mass of 
amorphous fragments with a few cells and shreds of fibre interspersed. 
Some idea of the quantity of. organic matter in Brown Muds and 
other loch deposits may be gained from the subjoined determinations 
of carbon. Six deposits were taken, namely : — 
(1) Loch Lurgain, 59 feet, a slightly sulphuretted Brown Mud. 
(2) Loch Frisa (Mull), 175 feet, a dark-coloured Diatom Ooze. 
(3) Loch Vevatie, 95 feet, a typical Brown Mud. 
(4) Loch Rannoch, 323 feet, a Brown Mud in an incipient stage 
of passing into Ochreous Mud. 
(5) Loch Gainmheich, 22 feet, a stiff brown Clay. 
(6) Loch Assynt, 23 feet, a typical Ochreous Mud. 
Of Nos. 1-5 the fine w^ashings were separated (coarse minerals 
insignificant except in No. 4, 20 per cent., and No. 5, 52 per cent.); 
No. 6 was dealt with as a whole ; the materials were dried at 110' C. 
Ignition losses were determined on one portion of each sample, and 
combustion analyses were carried out on another, with the following 
results : — 
No. 
Ignition 
Loss. 
By Combustion. 
Organic 
Matter. 
Carbon. 
Water. 
Loss. 
1 
27 '68 per cent. 
11-9.5 per cent. 
14-76 per cent. 
26-01 per cent. 
23-9 per cent. 
2 
18-27 
6-09 
13-51 
16-84 
12-2 
3 
37-08 
18-28 
19-87 
35-73 , , 
36-5 
4 
24-24 
11-60 
13-59 
23 06 
23-2 
5 
9-86 
2-82 
6-19 
8-43 
5-6 
6 
12-68 
1-26 
10-11 
11-34 
2-5 
The carbon in the vegetable matter associated with Brown Muds 
amounts roughly to 50 per cent. ; hence the figures in the last column, 
obtained by multiplying the carbon percentages by two, represent 
