10 



twenty-two feet. By collecting oysters from different depths 

 i* was possible to observe the limits within which the water was 

 iresh for a sufficient length of time to kill all the oysters, and 

 running down from this level to find the proportion of living 

 oysters at the different depths. All the oysters living above 

 low tide mark and those down to a depth of six feet below that 

 level were dead, while with an increasing depth of water the 

 proportion of living individuals increased rapidly, although, 

 even at a depth of sixteen feet many of them had succumbed 

 before the time Avhen the water became normal. 



TABLE 2. 



Percentage of living oysters at different depths on the 

 Jjighthouse reef, June 6, 1905 : 



Percent, of Percent. 



Depth of water. living oysters. hinged shells. 



Above low water mark 0.0 100.0 



3 feet 0.0 100.0 



6 feet 0.0 100.0 



30 feet 46.0 54.0 



12 feet 62.0 38.0 



ir feet 98.0 2.0 



The liquids contained within the shells of living oysters 

 froin any part of the pass were always considerably more saline 

 th.an the water in the river at the time these wc;re taken up, so 

 that it was apparent that the valves were opened only when the 

 water was at its maximum salinity. 



On the 6th of June the water in tho pass became salty as 

 far np as the lake, and from this date until June "^ ' the 

 salinity averaged /^^// at the laboratory wharf. 



After a heavy rain on June ^^-i^the water again became ab- 

 solutely fresh. From this date until late in October the water 

 was fresh, except for intervals of one or two days at a time, 

 when there would be brackish water in the lower part of the 



* Only those de:id shells, of which the hincres were intact showinsr that the 

 oysters h;id been dead ii short lime only, were counted in determining the percent- 

 ages tjiven in this table. 



