BIOLOGY OP THE OYSTER-GROUNDS OF SOUTH CAROLINA. 
341 
floating powers of the young become more marked as the saltness of the water in- 
creases. The experiment would not be an impracticable one, for fresh water-speci- 
mens might easily be arranged in a set of graduated densities by the addition of natural 
salt. Should it be shown, for example, that in water of 1.023 oyster fry would occur 
only at the surface, and that in water of 1.016 the young might be found pervading 
equally the water volume, there could be little doubt of the value of the view of gravity 
fixation. Circumstantially, however, many opposing facts render this view untenable 
as long as positive proof is wanting. 
(a) Spat has been sparingly found affixed to deep-water shells, but we must admit 
that it may have been attached before the host itself dropped into deeper water. 
( b) The second corollary certainly does not maintain. Notwithstanding the water 
becomes fresher in character, deep beds of single oysters do not become common in 
an increasing ratio. Such as are found rarely have spat attached, and in every way 
appear still to represent the dropped-off raccoons. 
(c) As the water becomes less dense, raccoon ledges do not disappear. Oyster 
ledges occur in WinyawBay, where the specific gravity of the water is as low as 1.010. 
(d) It is well known that a deep set forms naturally in some regions, as about 
Long Island, New York, where the specific gravity in some places is as high as 1.021; 
and, moreover, I have recently examined in Florida oyster rocks well covered with 
spat in water of a density of 1.025 and at a depth of 10 feet. 
Again, granting an unexpectedly delicate osmotic character to the young, it may 
be shown that, if the embryo float, it must keep at surface level; for as the specific 
gravity of the water is often the same at top and bottom, the embryo, if it sink a few 
inches, might equally well sink many feet. Heavy barges of the Coosaw Phosphate 
Mining Co. never draw less than a foot, yet their bottoms are bristling with oysters. 
2. The view that the swimming embryo is unable to effect a successful fixation in 
the deeper waters, on account of the slime-covered character of the bottom and the 
softness of the muddy bank, might readily be true of many localities examined. The 
stream bed of many water-courses is formed of the softest and lightest muddy ooze, 
into which an object, such as an oyster shell dropped as a collector, would unfailingly 
pass, sometimes to a depth of many feet, as experiments have shown near Port Boyal. 
This ooze layer is widespread in the larger river basins ; its extent and character 
render oyster-culture in its immediate neighborhood almost impracticable; it covers 
the river phospate rock with a layer sometimes 15 feet in thickness. There have been, 
doubtless, many cases where oyster-culture has been discouraged by the absolute fail- 
ure of plants made upon an insecure or shifting bottom. It is evident that the more 
surface the planted oyster can expose to the soft bottom, or, in other words, the larger 
and lighter the oyster, the more apt is it to survive, although its efforts in that direc- 
tion are not apt to improve its commercial quality. A number of specimens have 
been retained, showing how skillfully mud masses have been plastered into the oyster 
shell, forming, indeed, an intricate series of mud galleries honeycombing the shell. 
The general truth of this view as affecting bottom set is of course untenable, as is 
proved by the oyster -bearing piles. There are, moreover, many localities where the 
cleanliness of the bottom will compare favorably with that of the best grounds of the 
Long Island coast. 
3. The suggestion as to amount of silt carried in suspension, especially in deeper 
water, should be carefully considered. We must bear in mind the extreme delicacy 
