BIOLOGY OF THE OYSTER-GROUNDS OF SOUTH CAROLINA. 
337 
fragmental, water-worn, curiously packed together by ages of water action, often 
implanted mosaic fashion with shells vertical. A large, dark-colored, living clump is 
seen prominently on the beach, and smaller clusters are to be noted in a receding 
dark-dotted line. 
The portion of an oyster flat,* shown in Plate lxiii, is seen from the water side. 
The low, irregular banks of mud are capped with oyster clusters. The sides of the 
mud banks are extremely soft, engulfing and gradually stifling the raccoon clusters that 
fall from above. Many of the holes seen in the sides of the mud bank are the gradu- 
ally disappearing gravestones of buried oysters. The larger holes mark the breathing 
currents of sinking oysters that are stifling 6 inches below. The entire backbone of 
the mud bank will be found, by probing, to consist of dead shells around which the 
mud has gathered. Large living clusters, budding out from the bank, will in time 
form a peninsula, as seen in the plate. The sink-holes and draining-trenches are 
naturally of value, preventing the accumulation of mud upon the living raccoons. 
Marsh grasses encroach very slowly, forming dry land as they go, and limiting by 
their margin the line of oyster growth. 
The oyster island! (Plate lxiv) deserves a passing notice, occurring very often 
throughout small creeks draining marsh land, extremely noticeable, since nowhere else 
in the neighborhood are oysters plentiful. It furnishes an interesting example of the 
oyster’s powers of land building. In a region where steep and soft muddy banks have 
prevented oyster ledges from forming, a single cluster, anchoring on the shore by some 
chance, gives rise to an outcropping “island,” formed entirely of oysters 5 its frame- 
work of dead shells; its flat, dome-like summit bristling with living clusters. The 
island, accordingly, originating as a cluster attached to the soft bank, continues its 
growth as a small peninsula and pushes out into the sluggish stream. The stream 
current aids its formation ; its framework is firmly packed with gradually accumulat- 
ing mud; its growth broadens outward into a portly island of oysters, whose small 
and narrow peninsula beginnings (where the man in the picture is standing) are almost 
lost to sight. 
That the zone for the attachment of oysters f (Plate lxv) is, in South Carolina, 
between the levels of high and low water may be noted upon stakes and piling every- 
where. The maximum size and abundance of oysters, naturally attached, will be seen 
from the picture to be midway between tide marks. The significance of this zone of 
oyster attachment is hereafter discussed. 
THE OYSTER CLUSTER AND ITS ORIGIN. 
Raccoon oysters, in their physical character, as briefly shown, have grown in 
bunches, clumps, and interlocked colonies, with manifest purpose. To grow in clusters 
was the oyster’s successful expedient in its struggle for survival. Grown in clusters, 
in the first place, the oyster is less apt to sink in the stifling mud than if separate; the 
raccoon anchorage, moreover, is apt to be a firm one, at the same time holding the indi- 
viduals as high up from the mud as possible. Equally importantis the function of the 
cluster in allowing the greatest possible number of oysters to survive in the smallest 
possible surface space. 
* Skull Creek, January 13, 1891. 
t May River (Skull Creek Region), 1 mile from mouth of Skull Creek, January 12, 1891. 
t Sullivan Island, steamboat wharf, March 12, 1891. 
F. C. B. 1890—22 
