much sediment which, under former conditions, would be 

 swept out to sea. The deep channels separating the 

 flats appear to form the natural home of the local 

 oyster ; for many years Government looked upon such 

 beds as breeding reserves and limited fishing to one day 

 in the year and then only for some two hours. 



The specific gravity of the water has no special 

 peculiarity. As may be expected it approximates to 

 that of the open sea in its seaward section under ordinary 

 conditions ; during and after rains the salinity and specific 

 gravity fall, as is but natural, especially in the northern 

 and eastern regions. Bashford Dean gives the specific 

 gravity as 1*0189 at the end of August (that of the open 

 sea being about i'026y), but does not state the locality 

 of his observation. Schmarda, on the other hand, is 

 quoted as giving the salinity as higher than that of the 

 Mediteranean. Such discrepancy is easily understood 

 by anyone who has studied any large land-locked body of 

 water having imperfect communication with the sea ; a 

 reading of the hydrometer taken in bays remote from 

 the mouth after prolonged continuance of dry weather 

 will furnish a high figure, whereas one in a locality which 

 is effected by the entrance of river or flood water will 

 naturally give a very low one during and immediately 

 after a spell of rainy weather. We are safe in stating 

 that the salinity varies considerably in different sections 

 of the basin and at different states of the tide and 

 according to the season of the year ; a statement proved 

 by the fact that two of the diseases to which the oyster 

 is subject are recognised at Arcachon as due in the one 

 case to an excessive amount of fresh water and in the 

 other to excessive salinity. The former, doufain, is well 

 known and dreaded as the cause of great mortality ; the 

 latter, due to abnormal scarcity of rain, is declared to be 

 exceptional or rather that it scarcely ever is so severe as 

 to cause much loss. 



Taken generally it appears that upon the average the 

 specific gravity of the water of the basin is usually 

 slightly below that of the open sea. 



