RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 361 



that water. That is, caution is necessary even in these more positive 

 cases, especially when the amount of discovered fossil material is mea- 

 gre. 



Not only caution but the exercise of careful judgment is necessary 

 in other cases. For example, it will also be seen by referring to the 

 foregoing review that certain families, while most of its members are 

 confined to one kind of water, may have one or more representatives 

 in other kinds, and again that certain families may have representa- 

 tives in all the known kinds of habitable waters. In such cases as these 

 it is plain that all evidence afforded by fossil remains to be of any 

 value must be corroborated by other evidence. 



Still, the cases are very few in which serious doubt need be enter- 

 tained as to the true character of the water in which a given formation 

 was deposited. This is especially true if the fossil remains are suffi- 

 cient in quantity and perfection to approximately represent the whole 

 fauna that lived in those waters. Indeed, if the facts which are re- 

 corded on the preceding pages are borne in mind there need be no more 

 doubt as to what was the quality of the water in which any given for- 

 mation was deposited than might arise concerning any other geological 

 observation. 



