394 Scientific Noiices-^Geology. [Nov. 



Geology. 



16. On the Accuracy of the Inference that certain Formations have 

 been deposited from Fresh Water, deduced from the Organic 

 Remains found in them. 



Dr. Mac Culloch, in a very interesting paper, on the Possibi~ 

 lity of changing the Residence of certain Fishes, which appeared 

 in the 34th number of the Journal of Science, having shown, 

 that several species of salmon spend a large portion of their time 

 in fresh water ; that the smelt has been familiarised entirely to 

 fresh water, in which it has been kept for three years by Colonel 

 Meynell, in Yorkshire, propagating and thriving abundantly ; 

 that the pike is found in the Caspian Sea ; and that many other 

 fishes live and thrive indifferently either in fresh or salt water, 

 concludes with the following judicious observations : — 



" There is a subsidiary question arising out of these specula- 

 tions respecting the convertibility of the habits of marine ani- 

 mals, highly interesting to geology, and on which it will not be 

 out of place to say a few words, although unfortunately not much 

 solid information can be procured respecting it. This relates to 

 the power which many, perhaps all the vermes inhabiting shells, 

 possess of residing indifferently in salt or fresh water. It is 

 well known to geologists that with respect to many, if not all 

 of those deposits supposed to have been formed, like that of 

 Paris and of England, under fresh water, the question mainly 

 rests 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 recol- 

 lection of all the readers of this journal. It has also been 

 recently ascertained by M. Freminville, that 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 confirm the general presumption 

 which forms the basis of this communication, their general pro- 

 bability 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, 

 particularly if these bring down mud, and in these places the 

 water is scarcely salt ; yet they live also and propagate in abun- 

 dance on shores which receive no fresh water. The oyster is 



