OYSTEB BOTTOMS IN MATAGORDA BAY. 53 



market, and none were fat. It is probable that, were it not for the 



long periods of low water and the consequent mortality, a very 

 considerable proportion of the shores of the upper bay would be 

 fringed by a dense growth of oysters instead of the sparse growth 

 now existent. The same causes operate to restrict or inhibit the pro- 

 duction of marketable oysters on the crests of the reefs of the lower 

 bay. 



Even in those cases in which oysters have set in water deep enough 

 to insure them against more than temporary exposure they are placed 

 under conditions unfavorable as compared with those surrounding 

 their fellows that are never exposed. They can feed only when 

 covered by the tide, and the more constant this covering the greater 

 the opportunity to obtain an abundant supply of food. In waters 

 richly laden with the minute plants on which they feed it may be 

 possible for them to obtain in a few hours daily all the nutriment 

 required for growth and fattening, but in less fertile waters the 

 entire twenty-four hours may be none too long. 



With equality in other conditions, therefore, those oysters which 

 are constantly covered have advantages over those subject to ex- 

 posure, and notwithstanding the good character of the bottom in the 

 shoal er waters of the upper bay, oyster culture could not be under- 

 taken there with any prospect of success for precisely the same rea- 

 sons that have militated against the establishment there of permanent 

 natural beds. The prospective oyster culturist of Matagorda Bay 

 must seek some location in which the bottom is not exposed during 

 the low tides prevailing in winter. That such locations, presenting 

 the other desirable features also, are not hard to find will be shown in 

 the further discussion. 



CURRENTS. 



In the original scheme of the survey it was contemplated to make 

 systematic observations on the direction and velocity of the currents 

 in various parts of the bay, but upon arrWal on the ground it was 

 speedily appreciated that from the nature of the local conditions such 

 observations would have but little value, and no definite data could 

 be presented. Currents in bays and estuaries in general are mainly 

 conditioned by the tides, which in most regions have sufficient regu- 

 larity to establish well-marked and definite currents for each phase 

 of lunar influence, and for airy given stage of the tide there is a cor- 

 responding current constant in direction and within certain limits 

 more or less constant in velocity and duration. In Chesapeake Bay, 

 for instance, the Coast Survey is enabled to furnish data showing the 

 direction and average velocity of the currents for any given point and 

 stage of the tide, but in the portion of Matagorda Bay covered by the 

 present survey such predictions are absolutely impossible, owing to 



