175 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
Solway, are extensive sandbanks which are twice in every 
twenty-four hours exposed to the atmosphere. For instance 
nearly 100 square nautical miles of sand are exposed twice 
a day in the Morecambe Bay area. There are also high 
tides, with a rise and fall of over thirty feet in some places 
and tidal streams with a velocity of seven knots at high 
springs. In the fairway of the Channel the backward 
and forward surge of water due to the tides is about nine 
miles during springs, and about six miles during neaps. 
Near the land the distance traversed by the moving body 
of water greatly increases. 
When the sandbanks are exposed by ebb-tide during 
the winter and spring months they become cooled greatly 
by radiation and evaporation; and when next the flood 
water covers them the latter becomes chilled below its 
normal temperature. Further, when the sandbanks are 
exposed during the summer and autumn months they are 
heated, and when next the flood-tide covers them the 
water becomes warmed above its normal. ‘Therefore, 
the sea offshore at any one point is alternately warmer 
and colder as these water masses are carried backward 
and forward by the tides. If we could take daily tem- 
perature observations out from the mouth of Morecambe 
Bay, as, for instance, at Piel Gas Buoy, it would be 
found that the temperature would generally be lower 
during the flood-stream, and warmer during the ebb- 
stream, in the summer months, while an exactly opposite 
condition would be experienced during the winter and 
early spring. 
The effect of changes in the height of the tides would 
also be apparent, for the extent of sandbanks covered, and 
consequently the amount of heat received or lost by the 
flood water, would vary from neaps to springs; and since 
the velocity of the streams also varies during a tidal cyele 
