468 
Proceedings of the Royal Society 
Table I. 
Table II. 
Depth in feet. 
Density. 
Percentage of Salts 
Present. 
Percentage of Fresh 
Water Present. 
Percentage of Sea 
Water Present. 
Depth in feet. 
Density. 
Percentage of Salts 
Present. 
Percentage of Fresh 
Water Present. 
Percentage of Sea 
Water Present. 
0 
1-001 
0-09 
99 
1 
0 
1-001 
0-09 
99 
1 
1 
1-002 
0-45 
92 
8 
1 
1-001 
0-09 
99 
1 
2 
1-004 
0-62 
84 
16 
2 
1-001 
0-09 
99 
1 
3 
1-014 
1-96 
44 
56 
3 
1-001 
0-09 
99 
1 
4 
1-016 
2-22 
36 
64 
4 
1-001 
0-09 
99 
1 
5 
1-023 
3-10 
8 
92 
5 
1-001 
0-09 
99 
1 
6 
1-023 
3-10 
8 
92 
6 
1-017 
2-34 
33 
67 
7 
1-023 
3-10 
8 
92 
7 
1-020 
2-72 
20 
80 
In the coloured diagrams (Plate XIY.) the shades represent roughly 
the quantity of dissolved salts at each depth as deduced by calcula- 
tion on the assumptions — which are accurate enough for the pur- 
pose of diagrammatic representation — that the indications of the 
rough hydrometer are correct, and that brackish water is ocean 
water diluted with pure water. 
If in a river running directly into salt water the channel should 
gradually deepen as it enters the sea, so that there should he no 
obstacle to the entrance of salt water as the tide rose, and if at the 
same time it were so narrow as not to be in any sense an inlet 
of the sea, the conditions in it would be truly comparable with those 
of a river gradually merging into a firth. This is never the case 
so far as we have been able to ascertain, as a bar exists at the 
mouth of all rivers. As a consequence, the sea water enters by 
first rising to the level of the top of the obstacle, and then pouring 
down on the other side through the fresh water, and so produces a 
large volume of brackish or not fully salt water inside the bar. 
The action of the breakers over the bar or in the shoal water 
outside serves still more to effect mixture. Were it not for the 
great rapidity and volume of the Spey, the tide would probably 
produce a uniform brackish mixture at the mouth of the river, and 
a much less marked series of salinity strata farther up, than those 
that were observed. 
