34 



tile lower part of the bay near the passes to the Gulf the bottom 

 is composed mostly of sand ; but in the upper part it is made up 

 almost entirely of mud. In most places the mud is quite firm, 

 the places where the bottom is too soft to support oysters being 

 along the shores in the extreme upper part of the bay. The 

 salinity of the water in the southern part of the lake, for some 

 three miles from the passes to the Gulf, averaged 1.0189, whik 

 in the upper portion — north of the lower point of the chain of 

 islands separating the western arm — it was 1.0158. 



In the open part of the lake there are no oyster reefs, and 

 no dead shells are to be found in any amounts. Along the islands 

 separating this lake from Timbalier Bay, there are great banks 

 of shells thrown up by the action of the waves. Almost all of 

 the shells in these mounds are badly broken up and disinte- 

 grated, showing that the oysters have been dead for a consider- 

 able time, and no living oysters or well-defined hardened areas 

 were found in this vicinity. The extensive changes that are 

 known to have taken place in the topography of this region, make 

 it seem probable that these shells have come from the break- 

 ing up of oyster reefs that formerly existed here when this re- 

 gion was made up of nearly continuous marsh, cut up by small 

 bays and bayous, as was true within the memory of many of 

 the inhabitants of this section. With the washing away of the 

 marsh the oyster beds became exposed to the full sweep of storms 

 from the westward and were probably destroyed by the action 

 (I the waves. When the reefs were broken up the shells would 

 either be buried in the shifting bottom or thrown up on the 

 islands so that there would be nothing left to which spat might 

 become attached to re-establish the reefs even though there were 

 plenty of fry in tlie waters. 



In the upper part of the lake the danger of destruction by 

 stonns is much less, as the bottom is composed of less shifting 

 materials, and there is greater protection against all storms ex- 

 cept those directly from the south. 



The richness of the food supply varies very markedly in 

 different parts of the lake. In the southern portion, where tlie 

 bottom is sandy and the salinity of the water is high, the water 

 contains a much smaller number of the food forms than in 

 the northern portion where the bottom is soft and where the tidal 



