96 MR. G. 8. BRADY ON THE 
Wear, which it joins about a couple of miles above Sunderland 
Bridge. The burn itself is, like the Wear at that point, subject 
to tidal influence; but the adjacent pools, of which we have 
more particularly to speak, are above the level of high water at 
spring tides, though the ground on which they lie is stated in 
the maps of the ordnance survey to be liable to floods, and is 
indeed on that account claimed by the River Wear Commis- 
sioners as coming under their jurisdiction. The pools are 
separated from the burn by intervening spongy ground, so that 
all their saline constituents must be obtained either by the 
agency of these very occasional floods, or by percolation through 
the soil taking place at the highest spring-tides. The burn has 
cut for itself a deep and tortuous channel, well defined, and with 
almost perpendicular banks, from which the ground stretches 
away on each side in a flat expanse for a distance of about seventy 
yards, until it merges in the steep sides of the dene. On this 
expanse (measuring altogether 150 by 3850 yards) are situ- 
ated several small pools, irregular in shape, but uniformly very 
shallow, with one exception scarcely ever exceeding, I think, 
about six or eight inches in depth. Zoologically, we may divide 
them into three groups—the jirst comprising those which lie 
nearest to the river Wear; the second including all others 
situated on the south of the burn; while to the third belongs 
only one deeper and larger pool, which is on the north bank of 
the burn. 
The proportion of saline constituents in the water of the pools 
regularly decreases as we recede from the river, the quantities 
being as follows :—those of the first group contain 64 grains of 
chlorides in the fl. ounce—=1°3 per cent.; second, 43 grains=="95 
per cent.; third, -84 grains—"176 per cent. These quantities 
should, however, be taken only as approximations to the truth; 
they must be open to considerable variation according to the 
amount of rainfall and the frequency of very high tides. As 
regards their organized inhabitants the pools differ no less con- 
spicuously than in their inorganic constituents. I append a full 
list of the animals which I have found in each group, but for the 
present it will be sufficient to point out their most characteristic 
