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occur, in petrified ligneous substances. The instances which have 
been given of any fossil substances which had derived their form 
from the labours of the inhabitants of the world, at any distant 
period, are remarkably few, and do, indeed, all appear under cir- 
cumstances which render the actual existence of such petrifactions 
highly problematical. 
The substances which have been most frequently mentioned, as 
being of this description, are those which bear the form of logs, 
billets, posts, and planks. But, surely, when it is considered, that 
a rude resemblance may have been frequently sufficient to have 
given rise to this opinion, and that wood, long exposed to the 
weather, to alternate sunshine and wet, to agitation in water, and 
afterwards buried by some violent convulsion, must be broken into 
a great variety of forms, it is not at all improbable, that it should, 
in some instances, assume an appearance, that may lead to the 
suspicion of its having been subjected to the operations of art. 
The same observation must apply to many of those substances 
which have been supposed to have been stakes, posts, and piles, 
which have been driven in the beds of rivers, &c. Of this descrip- 
tion are the pieces of wood which have been frequently dragged 
up from the bottom of the Thames, and which have been supposed 
to have been placed there by the soldiers of Julius Caesar. One of 
these was in the possession of the late Duchess of Portland, and 
was purchased at her sale for nine guineas, by the late John Hunter, 
Esq. and is in the matchless museum, which, by the death of that 
gentleman, is now in possession of the Royal College of Surgeons 
of this city. An examination of this body tends to confirm my 
suspicion, that substances of this kind do not owe any thing of 
their forms to the labours of the Roman soldiers. This piece of 
wood, about three feet in length, the surface of which is broken 
into flakes, by drying, has exactly the colour, and general appear- 
ance, of bituminous wood. Now from the observations, already 
