OYSTER BOTTOMS IN MATAGORDA BAY. 15 



TYPES OF OYSTER BEDS. 



These beds may be divided into three general types — (1) long 

 reefs consisting of extensive long, narrow shell beds surmounted by 

 oysters, running at right angles to the currents and with marked 

 shoaling of the water over their crests; (2) short reefs and lumps 

 consisting of small deep shell beds bearing oysters, with usually no 

 great disparity between their long and short axes, and also marked 

 by abruptly shoaling water; (3) flat beds and patches without ex- 

 tensive deposits of shells, over which the depth varies but slightly 

 from that over the surrounding bottom. 



LONG REEFS. 



The long reefs are confined entirely to that portion of the bay 

 lying below the mouth of the Colorado River, and judged by their 

 size and structure they are undoubtedly the beds of greatest age. 

 With the exception of Dog Island Reef, which forms a practically 

 complete bulkhead, they all begin at or near the northwest shore and 

 end in the deeper water toward the tniddle of the bay. Dog Island 

 Reef probably originated in the same way, and its present condition 

 is but a completed or more matured stage of development. The 

 stiff, waxy, prairie loam which forms the inland shore is better 

 adapted to the support of cultch than is the sand of the gulf side of 

 the bay, which is more or less subject to shifting under the influence 

 of the storms and winds which sweep over the sandy peninsula. 

 Shells or other bodies lodging in the shallow water near the prairie 

 shore are therefore preserved for a longer period in a condition 

 favorable for the attachment of the minute floating fry of the 

 oysters, and once established the infant bed tends to grow by yearly 

 accretions. After the bed has become fairly established and begins 

 to rear its crest above the bottom, the tendency is toward the pre- 

 ponderance of growth at its outer end, where the currents sweep 

 most strongly and more perfectly clean the oysters and shells of all 

 deposits of mud and silt which would operate to stifle the tiny spat. 



It will be observed from an inspection of the chart that each of 

 these reefs has its long axis at right angles to the set of the currents. 

 Above Palacios Point the currents run generally in the direction of 

 the length of the bay, and Mad Island, Shell Island, and Dog Island 

 reefs therefore lie almost transversely to the parallel shore lines ; but 

 at Palacios Point the bay abruptly widens, the currents describe 

 more or less of an arc with the point as the center, and Half Moon 

 reef has grown along that radius to which the flow of greatest velocity 

 is related as a tangent. In other words, the reefs have followed the 

 usual law of development, growing most rapidly toward the strongest 

 current and less rapidly along their sides, where the currents slacken 

 16354—07 m 2 



