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LETTER XLVIIL 
CONCLUSION. 
I endeavoured, in the early part of our correspondence, to lay 
before you the opinions which were formerly entertained, respecting 
the substances which have been generally known by the name 
of extraneous fossils ; and also to give you a slight sketch of the 
history of the discoveries which have been made, concerning their 
nature and origin, we then entered upon an examination of such 
substances as appeared to be best designated by the term vegetable 
secondary fossils. A strict examination of these seemed to render it 
manifest, that their formation depended on a certain law of nature 
which decrees, that such vegetable substances as become buried 
so deep, as to prevent their being directly useful to man, either 
as timber, or as soil fitted to aid the growth of other vegetables, 
should undergo certain other changes, by which they should be 
rendered peculiarly fitted for supporting combustion, in the various 
modes necessary for promoting the comforts of mankind, and con- 
ducting the numerous arts of civilized life. 
In this new mode of existence we saw reason for supposing, that 
the combination which took place was such as to resist the decom- 
posing powers of almost every agent, except that of fire : manifesting 
the completion of the process, and evincing proofs of the most wise 
and providential arrangement. For here we perceived that a state of 
permanency was yielded to the substance thus formed; which sub- 
stance appeared to be intended for the use of man for a period of 
time, not only beyond our knowledge, but even beyond the reach 
of conjecture. On the degree of perfection to which this process 
