Thames and Medivay Outflow. 13 



fish leave in a northern direction and ultimately Lie back 

 towards their original spawning-ground. 



Now these data of migration, spawning and otherwise, do 

 not apply alone to one locality, but are equally applicable to a 

 wide east coast range. Cceteris paribns, they accord with what 

 has been observed in the great bight of the Moray Firth, in the 

 Tay and St. Andrew's Bay, the Forth and the Humber. Nay, 

 in spite of the easterly deviation of North Sea surface current, 

 as mentioned above, we have evidence in favour of the same 

 phenomena being partially applicable to the estuary of the 

 Thames, even though in the latter the ebb tide, by addition of 

 pent-up river water, flows longer and stronger than the flood. 



5. Efflux. The Thames and the Medway of a certainty carry 

 down an immense quantity of detritus mud and floating debris. 

 Part of the mud is deposited on the shores and shoals, or reaches 

 the creeks ; but of the lighter particles an immeasurable amount 

 is swept outwards and northwards by the very strong ebb tides. 

 This is markedly evident at the slack and turn of the tide, say 

 at the edge of the Maplins, the Mouse Light and the Oaze. 

 Then, as the undercurrent begins to creep up-stream, if the more 

 stationary surface water is examined, it will be found grumly, 

 crowded with buoyant material, and often alive with animal 

 forms feeding thereon. Doubtless the Crouch, the Roach, the 

 Colne and the Blackwater contribute their share of river 

 mixtures. But these are indeed scant in proportion to the 

 bulk transported by the Thames and Medway, where towns, 

 riparian factories and enormous river traffic concur to augment 

 their quota of effluent towards the estuary mouth. 



It may incidentally be remarked that this mud and super- 

 natant stuff is not altogether an unmixed evil so far as the fish 

 themselves and the fisheries are concerned. (See Sects. IV. and 

 XIV.) Also it is remarkable how relatively little mud there 

 seems to remain on the usual fishing grounds from the Nore 

 seawards. The heaviest particles would seem to intermingle 

 completely with the sands, which are nearly everywhere pre- 

 dominant. 



