CHAPTEK V. 



CONCLUSIONS TO BE DRAWN FROM FOSSILS. 



WE have already seen that geologists have been led by the 

 study of fossils to the all-important generalisation that the 

 vast series of the Fossiliferous or Sedimentary rocks may 

 be divided into a number of definite groups or " formations," 

 each of which is characterised by its organic remains. It 

 may simply be repeated here that these formations are not 

 properly and strictly characterised by the occurrence in them 

 of any one particular fossil. It may be that a formation con- 

 tains some particular fossil, or fossils, not occurring out of 

 that formation, and that in this way an observer may identify 

 a given group with tolerable certainty. It "very often hap- 

 pens, indeed, that some particular stratum, or sub-group of a 

 series, contains peculiar fossils, by which its existence may 

 be determined in various localities. As before remarked, 

 however, the great formations are characterised properly by 

 the association of certain fossils, by the predominance of 

 certain families or orders, or by an assemblage of fossil re- 

 mains representing the " life " of the period in which the 

 formation was deposited. 



Fossils, then, enable us to determine the age of the deposits 

 in which they occur. Fossils further enable us to come to 

 very important conclusions as to the mode in which the fos- 

 siliferous bed was deposited, and thus as to the condition of 

 the particular district or region occupied by the fossiliferous 

 bed at the time of the formation of the latter. If, in the 



