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. 
