1252 OYSTERS, AND ALL ABOUT THEM. 



The history of the oyster fisheries of Arcachon is not 

 less instructive. 



The Bay of Arcachon may be almost said to be made 

 for oysters. It has the shape of an equilateral triangle 

 nine or ten miles on the side ; and it debouches by a 

 channel, thirty fathoms deep at the mouth, situated at its 

 northermost angle, into the Bay of Biscay. The winds 

 and waves of this stormy region have thrown up a range of 

 high sand dunes along the western boundary, and these 

 dunes, covered with pines, shelter the bay from the vio- 

 lence of the westerly gales. The difference of height 

 between high and low water (ordinary tides) is fifteen to 

 sixteen feet. At flood tide the whole surface of the bay, 

 except an island in the middle (He des Oiseaux) is 

 covered, but at ebb tide the greater part is dry, except in 

 so far as it is traversed by narrow channels, varying from 

 forty to ten feet in depth, formed by the water as it retires 

 into the deep outer passage at the ebb, and returns at the 

 flood. 



The interspaces between the channels thus laid bare 

 at each ebb are called " cressats." The bottom is com- 

 posed of sand and shells, with more or less mud. The 

 quantity of the latter constituent is said to be gradually 

 increasing, and in many parts old oyster beds are silted up 

 and covered with mud. The salinity varies, being least in 

 the northern angle, where much fresh water flows in. 

 Elsewhere the saline constituents amount to 3 per cent or 

 more, and in hot and dry seasons they may exceed those 

 of the Atlantic water outside. 



M. Tolle says, in his report to the German Govern- 

 ment on the oyster fisheries of France :- 



" The cressats are the old oyster beds of Arcachon, 

 once thought to be inexhaustible, which yearly yielded 



