BIOLOGY OF THE OYSTER-GROUNDS OF SOUTH CAROLINA. 
343 
The following were the results: 
Locality. 
Sediment 
(grams per 
liter) . 
Surface : 
1. West bank 
0.70 
3. Midstream 
6. East bank 
. 72 
Deejjer : 
2. West bank 
1.00 
4. Midstream 
1. 00 
5. Midstream, bottom 
1.60 
7. East bank 
1. 40 
It is noteworthy that the greater proportion of the sediment is present in mid- 
stream, where oyster set does not occur, and that the minimum amount of sediment 
occurs at the marginal surface, where the oyster ledges are found. The exposure to air 
of these tidal reefs allows the sediment to dry and possibly gives the oyster an oppor- 
tunity to expel any ingested mud. My notebook states that the sediment from the 
marginal water is u extremely oily, clogging the fine filter paper, rendering the filtering- 
process an extremely slow one. The filtrate leaves a waxlike smear near the point of 
the paper funnel.” 
Enough has probably been said in this connection to show the necessity in prac- 
tical oyster-culture of collecting spat on floating collectors and of allowing it to attain 
before planting a considerable size, the larger the better. To plant successfully, the 
oysters should certainly be not less than 2 inches in diameter. The necessity of an 
unshifting and fairly solid bottom is of course obvious. If the collecting surface be a 
horizontal one, the under side will be found to collect the greatest amount of spat. 
This condition was found to occur in all of the natural floating collections examined. 
Barge bottoms as successful collectors have already been noted. All phosphate barges 
have yearly to be scraped of their compact, densely crowded set, the oysters within 
this time thriving remarkably, specimens 3 inches in length having been taken the 
present season (February, 1891) from the barges of the Coosaw Mining Company.* 
In this position the young oysters are in water bearing evidently the minimum amount 
of silt, and, from their down-turned position, least affected by the gradual depositing 
of sediment. 
4. The question as to variations in the composition of water at different depths 
tending to be of benefit to marginal oysters has proven a comparatively unimportant 
one. Marginal surface waters do not differ in composition materially from those deep 
in midstream, and therefore can offer no remarkable inducement to the formation of 
raccoon ledges. They are neither remarkably fresher nor richer in lime for shell build- 
ing; they offer no conditions of far greater abundance of food or greater freedom from 
impurities that might account for the absence of oysters in deep water. Neither do 
the tides appear to bring about any strikingly beneficial changes in the character of 
marginal waters. 
* Dr. C. Bunting Colson: “History of the Mill-Pond Oyster and Cause of its Disappearance”; 
Proc. Elliott Society, March, 1888. 
