so 



In a geological classification of rocks, it might 

 appear proper to have made a separate division 

 of those which are found in the several fresh- 

 water partial formations that have recently been 

 described. But our knowledge of these deposits 

 is as yet in its infancy ; nor are the rocks which 

 they comprise so different in character as to re- 

 quire a separate division. For the present, they 

 fall without inconvenience into the secondary 

 class. The principal interest attending these strata 

 is of a geological nature: and, indeed, depends 

 chiefly on that of the organic substances which 

 they contain. If future acquisitions of knowledge 

 respecting them should render it necessary, there 

 will hereafter be no difficulty in modifying the 

 present arrangement so as to give them an appro- 

 priate place. 



