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LETTER XXIII. 
OPINIONS RESPECTING THE FORMATION OF COAL EARTH IMPREG- 
NATED WITH PETROLEUM, THE OPINION OP BUFFON AND GEN- 
SANNE OPINION OF SIGN. ARDUINO, OF DR. HUTTON AND PRO- 
FESSOR PLAYFAIR, OP MR. WILLIAMS, OF MONS. TINGRY, OF DR. 
DARWIN, OF MR. KIRWAN, OF MR. HATCHETT, OF MONS. PATRIN, 
OF MONS. FOURCROY. 
Among the humiliating proofs of our limited powers of inquiry, 
there are few which are more striking, than that which is manifested 
by the inefficiency of our investigations relative to coal. Respect- 
ing the origin of this substance, so plentifully bestowed on us for 
our daily use, and consequently continually subjected to the im- 
mediate examination of our senses, the most widely different opi- 
nions have been held ; and by those, too, who have been the most 
competent to form a proper judgment. Even with that theory 
which has been the latest promulgated, by a gentleman whose ex- 
traordinary knowledge in mineralogy and chemistry stamps a high 
degree of authority on ev-ery opinion he adopts, I am under the 
necessity of expressing my dissatisfaction. 
This circumstance is the more unpleasant, since the observations 
which led to the objections to this ingenious theory, have also forced 
me to the adoption of an hypothesis, which, although sufficiently se- 
ductive to hold my judgment captive, may be found, by the more dis- 
cerning, to possess less probability than those opinions to which it is 
opposed. To enable you to form a judgment on this subject, I shall 
proceed to place before you those opinions which have been most ge- 
nerally adopted, and such objections as seem to affect their validity, 
VOL. I. H H 
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