23 



the luud, and there is uo longer any danger that the oysters 

 will be covered' by sediment, the elevation of the new area is 

 quite rapid. The tirst steps in the process are the slowest, as 

 the reef is at first composed only of a very few oysters. These 

 are attached to some hard body that has remained above the 

 mud long enough to enable the oysters to reach a size when 

 there would be no danger that they would be themselves covered 

 up and stifled. Of the total number of such small beginnings 

 i*^ is certain that only a very few come to be developed into reefs 

 of any size, while by far the greater number of them never 

 cover more than a few square yards at most. In regions where 

 the salinity of the water, and the abundance and distriDUTiou 

 of the food organisms, is such that the oysters would grow very 

 well, the number, size and location of the reefs, as well as the 

 quality of the oysters growing on them, depends to a great ex- 

 tent on the character of the bottom. In such a locality it is 

 usually found that the bottom in all places where it has not been 

 artificially hardened by the formation of reefs, consists of very 

 soft mud and the area bearing oysters is insignificant when 

 compared with the whole territory in question. It has also 

 been observed that the oysters making up these natural reefs 

 are, almost without exception, of very poor quality, long and 

 irregular in outline, very narrow, and with little depth between 

 the shells. Usually they will be found attached in clusters to 

 some shell of an older generation which is mostly below the sur- 

 face of the mud. At the time when the oysters of the last 

 generation settled down to their fixed life, the shells of their 

 parents afforded the only pla'oes for attachment in the vicinity, 

 and by the growth of the younger oysters the older ones have 

 been covered up so that they could not get an abundance of 

 food. Besides, the sediment settles out from the water as the 

 surrents are slowed down by the shells of the younger generation 

 rising above their parents. If one of these clusters is examined, 

 it will frequently be possible to count from three to seven gen- 

 erations in a single cluster, each generation being attached near 

 the upper end of the shells of the preceding one. This charac- 

 teristic shape of the oysters from a natural reef which has never 

 been M-orked is due to the crowding that takes place among the 

 f)ysters in the struggle to keep the upper, open ends of the 



