Distribution of the Common Oyster. 187 
appear to be otherwise favourable, as no fishery has been esta- 
blished there. 
It may therefore be said, with justice, that the oyster 
inhabits the shores of Europe so far as these are touched 
more or less directly by the Gulf-stream, reaching northwards 
as far as the polar cirele—the Channel and the south coast of 
England forming the centre of its distribution. 
That the oyster does not occur on the shores of Iceland or 
the Feeroes, is interesting in so far as it shows that its diffu- 
sion is due to the facility with which the spat is carried on by 
the current. No current coming from the English or other 
Kuropean coasts, and by which spat might be brought, im- 
pinges on the shores of Iceland or the Faroe Islands; the 
waters of the Gulf-stream by which they are washed come 
direct from the channel of the Bahamas. 
If it be granted that the oyster has been carried to its pre- 
sent stations by the various branches of the Gulf-stream, it 
may be concluded that its specific centre is the place where 
that stream first reaches the continent of Hurope, viz. the west 
coast of Spain, from which it has afterwards spread south- 
ward into the Mediterranean, and northwards as far as the 
olar circle. This, again, would be a point to be considered 
in settling the question as to the physical conditions accom- 
panying the deposition of the Crag formation in England 
and the strata north of Gothenborg near Uddewalla, in which 
oysters occur in a fossil state. 
ut though oysters occur along the whole of the line indi- 
cated, they are by no means equally plentiful or well-developed 
atall points. Oyster-banks occur in many places, even as far 
north as Bergen in Norway; but those along the shores of 
England and France seem by nature to be the richest. On 
these banks, which are situated at varying distances from the 
shore, and where the oysters live in the pure water entering 
from the Atlantic, having a saltness of 3°5 or 3°6, they grow to 
a good size and produce many young; but they do not reach 
that fulness and delicacy which is obtained by moving them 
from the breeding-places to other localities exhibiting cer- 
tain peculiar conditions. The places where oyster-culture 
succeeds have this in common, that they are protected by 
islands or shoals against the immediate influence of the 
open sea, and that the sea-water is diluted by the fresh water 
of rivers charged with a quantity of organic matter, which 
affords nourishment to the oysters. ‘I'ransferred to such places 
the oyster is considerably improved in size and taste; the 
liver 1s more particularly increased ; and the shells become 
more regular, because the animals are so openly scattered as 
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