Uniformity in Geological Change 



of this machinery, I shall compare it to a some- 

 what analogous case that might 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 grad- 

 ually taking place everywhere, suppose commis- 

 sioners 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 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 contents of 

 such as stand next to each other will differ ac- 

 cording to the length of the intervals of time 

 between the taking of each census. If, for ex- 

 ample, 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 in- 

 habitants, during the interval between the com- 

 piling of two consecutive documents, that the 

 individuals described in such documents will be 

 nearly identical; whereas, if the survey of each 

 of the sixty provinces occupies all the commis- 

 sioners for a whole year, so that they are unable 

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