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ture of wood. That the mere earthy particles of a vegetable should 
thus abide together, and continue in their original form, after being 
deprived of those particles, by which they had been held together ; 
and that they should, even after the total removal of these con- 
necting particles, instead of becoming displaced themselves, stem 
the percolating particles of earth, and be able so to retain them, 
that they should, combined, faithfully represent, as many specimens 
do, the original peculiarity of structure of the wood, was an opinion 
fraught with so many obvious difficulties, that another mode of 
explanation was soon adopted. 
The next theory which was proposed, with the hope of ac- 
counting for these changes, was that of a substitution of stonv, 
in the place of the organized matter, which was supposed by many 
of those who adopted this opinion, to be intirely removed. Thus 
Berthold says, petrifaction is not a metamorphosis into stone, but 
a removal, by putrefaction, or precipitation, of the vegetable or 
animal matter; and a substitution of stony matter, in the same 
rnanner as happens, in metals — copper being, for instance, some- 
times thus substituted in the place of iron*. M. Walch also, in 
the supplementary part of Knorr’s splendid work on this subject, 
declares his adoption of this opinion to its fullest extent. Different 
species of petrified woods, he says, teach us that all the particles, 
even the finest, constituting the substance of any extraneous body, 
may successively disappear, and be replaced by foreign heteroge- 
neous particles, with so much regularity, that the body, which is pro- 
duced from them, may possess, perfectly, the form of the original 
body, preserving all its characters, and at the same time not re- 
taining any at all Caucune de toutesj of its original particlesf. To 
* De Kebus Petrifactis, &c. — b. Dan. Gothilf. Bertholdo. 1766. 
t Eecueil des Monumens des Catastrophes que la Globe de la Terre a essui6s, &c 
commence par Mons. Wolfgang Knorr, continue par ses H^ritiers, avec I’Histoire Naturelle de 
qes Corps, par Mons. Jean Ernest Emanuel Walch, 1775, tome iii. Pr^f. 
