IX GEOLOGICAL CONTEMPORANEITY 275 



But this is not all. Allied with geology, '/. 

 palaeontology has established two laws of inestim- 

 able importance : the first, that one and the same 

 area of the earth's surface has been successively 

 occupied by very different kinds of living beings ; 

 the second, that the order of succession established 

 in one locality holds good, approximately, in all. 



The first of these laws is universal and irre- 

 versible ; the second is an induction from a vast 

 number of observations, though it may possibly, 

 and even probably, have to admit of exceptions. 

 As a consequence of the second law, it follows 

 that a peculiar relation frequently subsists between 

 series of strata containing organic remains, in dif- 

 ferent localities. -The series resemble one another 

 not only in virtue of a general resemblance of the 

 organic remains in the two, but also in virtue of a 

 resemblance in the order and character of the 

 serial succession in each. There is a resemblance 

 of arrangement ; so that the separate terms of 

 each series, as well as the whole series, exhibit a 

 correspondence. 



Succession implies time ; the lower members 

 of an undisturbed series of sedimentary rocks are 

 certainly older than the upper; and when the 

 notion of age was once introduced as the equiva- 

 lent of succession, it was no wonder that corres- 

 pondence in succession came to be looked upon as 

 a correspondence in age, or "contemporaneity." 

 And, indeed, so long as relative age only is spoken 



