Ch. III.] OF ORGANIC REMAINS. 31 



strong grounds for conceiving that such is the order of na- 

 ture. 



Fossilization of Plants and Animals partial. We have 

 seen that the causes which limit the duration of species are not 

 confined, at any one time, to a particular part of the globe; 

 and, for the same reason, if we suppose that their place is 

 supplied, from time to time, by new species, we may sup- 

 pose their introduction to be no less generally in progress. 

 Hence, from all the foregoing premises, it would follow, that 

 the change of species would be in simultaneous operation every- 

 where throughout the habitable surface of sea and land ; 

 whereas the fossilization of plants and animals must always be 

 confined to those areas where new strata are produced. These 

 areas, as we have proved, are always shifting their position, so 

 that the fossilizing process, whereby the commemoration of 

 the particular state of the organic world, at any given time, 

 is effected, may be said to move about, visiting and revisiting 

 different tracts in succession. 



In order more distinctly to elucidate our idea of the working 

 of this machinery, let us compare it to a somewhat analogous 

 case that might easily be imagined to 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, suppose 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 inhabitants, and leaving in each district a register con- 

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

 of one census, another is immediately made after the same 

 plan, and then another, there will, at last, be a series of 

 statistical documents in each province. When these are 

 arranged in chronological order, the contents of those which 

 stand next to each other will differ according to the length 

 of the intervals of time between the taking of each census. 



