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It is well known that shell-fish of all kinds thrive best when 
the supply of lime is greatest. The fresh-water mussels which 
live in streams and ponds where the supply of lime is scanty, 
grow slowly, and their shells are so thin that they are very 
subject to accidents, and their numbers are limited ; but in 
limestone regions the shells are large and heavy, and the bot- 
toms of the streams are almost paved with mussels, and it is 
well known to conchologists that coral reefs and islands are 
the most favorable regions for the abundant growth of all 
kinds of shelled molluscs. 
The dead oyster-shell is soon corroded, and in a few years 
entirely dissolved, by the sea-water; and I think this fact is 
another reason why the young oysters thrive best on a natural 
oyster-bed. 
How far the supply of oysters is limited by the supply of 
lime it is impossible to say ; but when we recollect how im- 
portant it is that the young oysters should scion find solid 
bodies to fasten themselves to, and that they should protect 
themselves by strong shells of their own as quickly as possible, 
it will be seen that the danger of exterminating a natural bed 
by over-dredging would be much less if the empty shells were 
replaced upon the bed. There can be no doubt that the best 
natural beds may be destroyed by over-dredging, and that this 
fate will be certain to overtake the beds of the Chesapeake 
Bay if the oyster industry continues to increase, and matters 
are left to adjust themselves. 
Like most dangers, this is one which will not become con- 
spicuous until it is too late to find a simple remedy. 
Whether the number of oysters which are at present taken 
from our oyster beds is too great or not is a matter which is 
outside the field which I undertook to investigate, but it is a 
matter in which the public have the greatest interest, and the 
extent of the oyster beds, and the number of oysters which 
they can supply each year, should be accurately ascertained 
before it is too late. 
A prophet of future evil is always regarded as an unseason- 
able croaker, but the facts which I have noticed seem to show 
that, whether the danger of exterminating the best and most 
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