XVII.] GEOLOGY OF THE THAMES BASIN. 277 



which ranges from tlie Norman conquest to the sixteenth 

 century. Hence it might be concluded that the pavement 

 B, was put down, at least as late as the sixteenth century ; 

 and this inference is confirmed by the fact, that such a 

 pavement was known to exist in the locality, before the 

 great fire of 1666. 



Thus it will be observed, that the general conclusions de- 

 duced from the character and contents of the successive beds 

 of made ground in Cannon Street, are fully borne out by 

 independent evidence ; and, if nothing were known of the 

 ancient history of England, beyond such archaeological facts 

 as these, they would leave no doubt a-s to the fact, and the 

 relative age, of the Roman occupation. 



The principles, on which the interpretation of the Cannon 

 Street section rests, are two : ist. In such cases as that under 

 consideration, the uppermost stratum is the latest formed, 

 and the lowest, the oldest. 2nd. The similarity of bodies 

 having a definite form and structure is presumptive evidence 

 of the similarity of their origin. It is the former principle 

 which justifies the conclusion that the pavement B is older 

 than the pavement D ; it is the latter, which leads us to 

 say that a piece of pottery is Roman raiher than English. 

 All the conclusions as to the history of the earth, deduced 

 from the structure of its crust, are based upon analogous 

 principles. If certain strata can be shown to have been 

 deposited by aqueous agencies, then the uppermost of these 

 strata is the newest, and the undermost is the oldest. If 

 the fossils which are embedded in these strata can be 

 proved to be similar, in all essential respects, to the hard 

 parts of living animals and plants, then they are evidence 

 of the existence of such animals and plants, antecedent to, 

 or during the deposition of, these strata. 



On referring again to the Cannon-Street section, it is seen 



