478 
Proceedings of the Royal Society 
course of the burn. Although there is no apparent outlet, close 
examination shows that an immense number of trickling streamlets, 
varying in breadth from half an inch to about a foot, and in depth 
from that of a mere film to several inches, escape all along the lower 
margin of the hank, and meander across the sand to the sea, the 
edge of which is perceptibly freshened by this means. The condi- 
tion of outflow is represented in the diagram, Plate XY. fig. 4, 
fresh water by a red, sea water by a blue colour. 
The variation of salinity with depth throughout Spey Bay depends 
almost entirely on the amount of flood in the river, and on the 
direction in which it runs. On August 10, when the river was 
low, and the boat in cruising about the bay did not encounter any 
freshened surface water, there was, as a rule, a uniform and slight 
increase of density with depth; while on August 18, when the 
river was flooded and the surface water of a great part of the bay 
comparatively fresh, the bottom and half-depth densities remained 
as before, and the surface was greatly freshened, although to a slight 
depth. One or two cases were observed where the water from half 
the depth was denser than that from the bottom, and ono in which 
it was less dense than at the surface. These differences may be due 
to irregular and incomplete mixing of river and §ea water. 
The course of the fresh water stream through the bay is beauti- 
fully seen during a flood. Fishermen fold us that when a heavy 
spate occurred with a southerly gale they have seen the coloured 
water running due north in a wide stream, but that if usually runs 
towards the east. 
A great spate occurred on the night of August 12, the largest, 
according to the ferryman at Garmouth, for over fifteen years. The 
average state of the water during our stay had been lower than it 
had almost ever been observed before. On the morning of the 12th 
the river was low, and the water very clear and perfectly colourless. 
At 17 h .30 the water had a clear amber colour, was very slightly 
increased in volume, and had the temperature 50° ‘0. Xext morning 
(August 13) the river was a broad sheet of leaping yellow waves, 
sweeping from bank to bank, and carrying down planks, salmon 
boxes, and potatoes, a field of which had been flooded and destroyed 
some miles up the river. As the current crashed round the shingle 
heaps with tremendous velocity great slices of the bank, from a few 
