342 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
of tlie breathing arrangements of the young oyster, as pointed out by Prof. John A. 
Ryder, and it is to be remembered that injury to the young caused by silt-bearing 
water was the cause of the failure of the most careful experiments upon the artificial 
propagation of the oyster. 
Along the South Carolina coast the question of silt suspension becomes of very 
great interest in the light of geology. Formations are here found (phosphate rock, 
marls, and fish-bone beds) that in richness of fossils and in extent are curiously 
unique. For ages the coast regions within the limits of South Carolina must have been 
a collecting basin or sink, receiving the washed-out drainings of hundreds of square 
miles. That the fresh waters of the State are still carrying seaward an amount of 
silt greater perhaps than occurs elsewhere to the. north or south, great enough, indeed, 
to stifle frail microscopic oysters, is therefore in no way remarkable; that flats and 
shoals are changing and forming constantly and rapidly in rivers and river mouths 
by the gradual settling of the heavier sediment is abundantly proven. 
In the water, at the surface, middle, and bottom, at every locality examined, there 
is present, in a more or less marked way, a heavy sediment, although the water itself 
has appeared clear. This sediment is exceedingly fine, in the surface water often 
requiring three days to settle. So very gradually is it deposited that the living organ- 
isms in the water will seldom be thrown down and included in it. It consists of the 
microscopic particles of clay and silica and, to my surprise, of the fossil tests and 
fragments of tests of the diatoms of the Ashley group. The occurrence of these fossils 
is, however, under the circumstances a very natural one. My attention was first called 
to the recurrence of numbers of dead shells of Coscinodiscus radiatus , for which I was 
at a loss to account. This form I remembered occurred fossil, as well as recent, and 
the finding in this genus of radiolatus and granulatus and many other well-known 
forms confirmed my decision. It is evident that the amount of this impalpable sedi- 
ment may vary greatly from natural causes, and the variation in the turbidity of river 
water is sometimes quite remarkable. There can be little doubt that this silt is in- 
jurious to the young oyster, and its presence in quantity may readily suffice to account 
for the entire absence of oyster spat in deep water. The greater the volume of the 
water mass, the greater would, of course, be the amount of suspended silt; the nearer 
the surface the less silt, and conversely. 
The amount of silt in a given specimen may readily be determined with a fair degree 
of accuracy, but it is impossible to learn whether the results obtained are relatively 
great or small, since I can find no standard of comparison. However, I give in brief 
the results of the following experiments. A stream section across the Ashley, just 
below the drawbridge, was selected.* Specimens of water were taken on March 11 
from midstream and on the margins, in a fathom of water, at the points numbered in 
the diagram. Five hundred cubic centimeters of each specimen were shaken and care- 
fully filtered, and the filtrate then dried and weighed. The weight doubled gave the 
weight of sediment per liter. 
Beds of raccoon oysters are abundant there. 
