344 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
With a view to tlie examination of these questions, analyses were made of water 
specimens collected at such points as to represent the entire section of a stream. 
Thus, in the accompanying diagram, representing a theoretical stream section, water 
specimens would he collected by means of the water cup at each of the positions num- 
bered 1 to 11. A set of specimens, thus representing the character of the cross section 
of the stream, would be collected at the half tides and at high and low tide. The col- 
lection and analyses of specimens would be so arranged that, in point of time, the 
comparison of tides might be as accurate as possible. 
For a more complete comparison three sets of such examinations were made at 
different localities; one, near Beaufort, South Carolina, of a typical river mouth with 
deep water; a second, of a neighboring shallow, oyster-bearing stream; and, finally, a 
similar section over the raccoon beds of the Ashley River in the neighborhood of Charles- 
ton. The variations in the results, as seen in the appended tables (pp. 357-361), were too 
slight to be of practical importance. Comparative study shows, however, that changes 
in water layers do occur, changes that if more marked would tend to favor somewhat 
the growth of marginal rather than of ledge oysters, thus : 
(a) Saltness, as a rule, slightly increases with the depth of water. There appears, 
however, to occur (a foot or two below the surface) a stratum slightly salter than the 
water immediately above or below it. Extreme marginal waters are least salt, having 
per gallon about in weight less of chlorides than in deep water. 
(b) Carbonates (lime) increase with the depth of water. 
(c) The amount of salty and limy ingredients are, in the localities examined, but 
little affected by the changes of tides. 
(d) The greatest amount of decaying organic matter appears to be carried in the 
deeper midstream. The water is there most impure at low tide and purest at high 
water. The extreme marginal waters show a noticeable increase of impurities, evi- 
dently from surface drainage. 
(e) The most noteworthy variation shown by the analytic study will be seen in the 
organic element of the water, representing in general oyster food. The greatest amount 
appears almost invariably to occur in marginal waters near, and a fathom or two 
below, low- water mark. In the South Carolina waters examined the marginal waters 
appear (probably from the character of the bottom, higher temperature, and less rapid 
current) to .afford the best conditions for the attachment and rapid increase of minute 
plant life. As nearly as the organic results can be determined, it would appear, with 
due allowance, that marginal waters contain double the amount of oyster food found 
in midstream. Tides appear to have but a slight effect upon increasing or diminish- 
ing the amount of oyster food. The best feeding conditions of the water are during 
the rising of the tide, which appears to carry shoreward from the deeper waters a 
number of pelagic forms. High tide contaius the next highest percentage of oyster 
food. The poorest feeding conditions are shown at low water. 
