considerable influence upon the channels in the north- 

 western section. 



The sea outlet is extremely narrow, scarcely 3 kilo- 

 metres wide, and this again is so obstructed by sand 

 banks that the effective navigation channel has no 

 greater width than 170 yards. As a consequence of the 

 narrowness of the outlet and the obstruction caused by 

 the presence of extensive sand banks in the fairway, the 

 tidal outflow is retarded ; a considerable body of water 

 never drains out on any ebb and the tide cannot rob the 

 basin of its total spatfall as is liable to happen at less 

 favoured oyster centres where the ebb runs out through 

 wide and more or less unobstructed passages. 



The banks of the basin are of shifting sand in the 

 western section, rising sharply into high dunes thickly 

 clothed with pine trees. In the eastern section the banks 

 are low and marshy, composed of marl and mud brought 

 down chiefly by the Leyre whereof the delta has advanced 

 according to historical evidence about 1 kilometre within 

 the last ten centuries. Advantage has been taken of 

 the network of small channels formed in this deltaic 

 region to construct numerous fish farms, reservoirs a 

 poisson, of considerable economic value and several of 

 very extensive area. 



The flats or crassats which emerge at low tide are 

 composed of a basis of muddy sand, stiff and well 

 consolidated, overlaid generally by a thin layer of mud. 

 Towards the margin as the flats shelve abruptly into the 

 bounding channels the mud deepens to such an extent 

 that the workers have to use special shoes or sandals 

 having large wooden plates attached to enable them to 

 walk over it ; the higher levels of the flats form the bulk 

 of the oyster culture area, the firm surface facilitating 

 operations. Of recent years complaints have become 

 numerous of a marked increase in the amount of sediment 

 deposited upon many of these grounds particularly in the 

 eastern and northern sections of the basin and it would 

 appear as if the tidal scour were being interfered with by 

 some agency to such an extent as to retain in the basin 



