the Residence of certain Fishes. 231 
on this, namely, whether the shells now supposed, from certain 
analogies and peculiarities of structure, to have been inhabitants 
of fresh-water lakes, may not have equally existed in salt lakes, 
or even in the sea. Some experiments towards the elucidation of 
this subject have been instituted in France; but I need not detail 
them, as they must be fresh in the recollection of all the readers 
of this Journal. It has also been recently. ascertained by M. 
Freminville, thet in the gulf of Livonia, the shell fish which 
usually inhabit the sea, and those which belong to fresh waters, 
are found living together in the same places. While these con- 
firm the general presumption which forms the basis of this come 
munication, their general probability is also strengthened by that 
analogy. A few facts of common occurrence on our own shores, 
seem to add additional weight to the opinion that the testaceous 
fishes in general are not rigidly limited to one kind of water, but 
are capable of living in both. 
On our sea coasts, the common muscle is invariably larger and 
fatter at the entrance of fresh-water streams into the sea, par 
ticularly if these bring down mud, and in these places the water is 
scarcely salt; yet they live also and propagate in abundance on 
shores which receive no fresh water. The oyster is transported 
from the sea to brackish water, where it also, not only lives, but 
improves in condition. In the same manner the common cockle 
inhabits indifferently the muddy sand-banks near the exstuaries 
of rivers, which are always soaked with fresh water, and those 
sandy or half muddy shores where no such water isfound. These 
are by no means the whole of the instances which might be enu- 
merated in support of an opinion, of which the determination is 
so important in the present state of geological science; but as this 
subject is too important to pass lightly over, and as the bounds 
of this communication are already exceeded, I shall leave it to 
those who may have the means and the inclination to examine it 
in greater detail. I will only add, that the same considerations 
will lead to similar doubts, where it has been attempted by geolo- 
gists to determine the nature of strata, as to their marine or fresh 
water origin, by that of the remains of fishes found in them. 
