2 56 THE GREAT BARRIER REEF. 



on a sufficiently extensive scale for the practical application of the above suggestions, in the estuary 

 of the Endeavour River, in the neighbourhood of Cairns, and at the mouths of the several creeks 

 debouching into Port Denison, in the neighbourhood of Bowen. It may be here mentioned that 

 the foregoing variety of mangrove-oyster grows so luxuriantly in favourable localities in the 

 neighbourhood of Rodd Harbour, that as many as twenty or thirty two-bushel bags, suitable for 

 cultivation on the banks, have been gathered from a single tree. 



The collective growth forms of Ostrea glomcrata, known as dredge and drift oysters, remain to 

 be noticed. The first-named title is applied generally to all oysters growing below the level of 

 usual ebb-tide, that of drift oysters being more exclusively associated with those lying loose and 

 separately at the bottom of the water, and which are supposed to have been washed from the 

 banks or beds, and to have drifted here and there at the mercy of prevailing currents. The tend- 

 ency of the dredge, or deep-water, oyster to develop a more elongate shape with a much smoother 

 and less crenulated marginal border has been referred to on a previous page. With the typical 

 " drift" variety the tendency to develop an abnormally massive shell, through continued erosion, is 

 especially noteworthy, instances occasionally occurring in which the lower, or right, valve weighs 

 as much as half a pound avoirdupois. The concavity of such a shell is rarely of sufficient size to 

 contain more than a single fluid ounce, while the corresponding shell of a fine, cultivated "bank " 

 oyster, having an internal capacity of two fluid ounces, yields an average weight of scarcely three 

 ounces. Dredge and drift, as compared with bank, oysters contribute to a less extent to the oyster 

 trade of Queensland, the relative proportion, so far as it can be ascertained, while formerly 

 considerably larger, being now about 20 per cent. In this respect, the Queensland oyster fisheries 

 present a marked contrast to those of the neighbouring colony of New South Wales, in which 

 the dredge and drift varieties have, until within recent times, represented the most important com- 

 mercial factor. Among the arguments that have been advanced in favour of the specific distinct- 

 ness of the deep-water oyster, or Ostrea subtrigona, as it is designated by those who advocate its 

 distinction, is the one that this deep-water form will not live if transported to the tidally-exposed 

 banks, any more than will the bank variety if consigned to deep water. If the transition is made 

 unseasonably, unfavourable results are likely to ensue. Where the change is judiciously effected, no 

 difficulty is experienced in cultivating dredge or drift oysters on the ordinary banks, or vice versa. 

 In various localities in Moreton Bay, and notably at the Breakwater in Nerang Creek, oysters 

 grow in a continuous sloping series, from a depth in which they are covered by a fathom or more 

 of water to the tops of rocks that are dry with every ebb. Oysters taken from these exposed rocks 

 are, moreover, systematically and successfully laid down as "cultivation " on a neighbouring dredge 

 section, where they are covered by at least two fathoms of water. No more practical evidence, 

 probably, could be adduced, in demonstration of the specific identity of the deep-water and tidally- 

 exposed series. Parallel examples of a species of oyster adapting itself to the varied conditions 

 of either total or partial submersion, are afforded by the typical European oyster, Ostrea ediilis, or 



