If 



' 



V 



a 

 i 





m 



d. 





ll: 



tl 



■ 



- 



re. 



er- 



xl 



* 



.an 

 of 



lier 



be- 



311- 



L 



el- 



em 

 en- 

 nd 



• 



we 



for 



i 



i 



t« 



?if 



Ch. XIV.] 



THE SEQUENCE OE FORMATIONS. 



°21 



where throughout the habitable surface of sea and land ; 

 whereas the fossilisation of plants and animals is confined 

 to those areas where new strata are produced. These areas. 



as 



we have seen, are always shifting their position, so 



liiacliinery, i snan compare 



that miffht be imagined to 



that the fossilising process, by means of which the comme- 

 moration of the particular state of the organic world, at any 

 given time, is aifected, may be said to move about, visiting 

 and revisiting different tracts in succession. 



To make still more clear the supposed working of this 



It to a somewhat analogous case 

 occur in the history of human 

 affairs. Let the mortality of the population of a large country 

 represent the successive extinction of species, and the births 

 of new individuals the introduction of new species. While 

 these fluctuations are gradually taking place everywhere, sup- 

 pose commissioners to be appointed to visit each province of 

 the country in succession, taking an exact account of the 

 number, names, and individual peculiarities of all the in- 

 habitants, and leaving in each district a register containing 

 a record of this information. If, after the completion of one 

 census, another is immediately made on the same plan, and 

 then another, there will, at last, be a series of statistical 

 documents in each province. When those belonging- to any 

 one province are arranged in chronological order, the con- 

 tents of such as stand next to each other will differ according 

 to the length of the intervals of time between the taking; of 

 each census. If, for example, there are sixty provinces, and 

 all the registers are made in a single year and renewed 

 annually, the number of births and deaths will be so small, 

 in proportion to the whole of the inhabitants, during the 

 interval between the compiling of two consecutive docu- 

 ments, that the individuals described in such documents 

 will be nearly identical ; whereas, if the survey of each of the 

 sixty provinces occupies all the commissioners for a whole 



year, so that they are unable to revisit the same place until the 

 expiration of sixty years, there will then be an almost entire 

 discordance between the persons enumerated in two consecu- 

 tive registers in the same province. There are, undoubtedly, 

 other causes besides the mere quantity of time, which may 



vol. i. 



7 



