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in cons6(^u6nc6 of tho fragility of tho iticlosod. body boing suchj that 
it is almost always very much shattered by the blow which is necessary 
to break the pebble which incloses it. In the meantime, the regularity 
and constancy of the form which it bears in the multitude of its 
specimens which may be met with, is no small proof of its having- 
derived its form from some organized being. 
The constant uniformity of the figure which this substance bears 
is by no means offered as a proof alone of its animal origin ; since, as 
in the instance of the Ketton and other stones, a constant unifonnity 
of figure is observable, without any reason appearing for supposing 
them ever to have existed but as minerals. A circumstance, however, 
is observable in these pebbles, as has been already slightly noticed, 
which at least proves three distinct stages in their formation; and 
also tends to confirm the suspicion of the inclosed body having existed 
in a distinct state. The openings in the pebble, through which 
the processes have passed, plainly shew that this body must have 
previously existed, and that it has been a nucleus, on which the sur- 
rounding silicious matter has been deposited. Those marks in the 
pebble, too, where traces only of these openings can be seen, the 
openings themselves being filled up by silicious matter, shew that an 
addition of this silicious matter, in a fluid state, has been made, after 
the pebble had been formed round this nucleus, and after the projecting 
bodies, which had filled those openings, had been removed by some 
force. 
At Fig. 14, a representation is given of the appearance which some 
pebbles derive from this body. It is at the wide superior extremity, 
where the processes have passed, that meandering lines are disco- 
vered. These seem to have been formed by the concurrence of the 
edges of two or three openings, which have been filled up by silicious 
matter. 
I am fully aware of the scepticism with which my conjectures on the 
nature of the preceding fossil will be received : that a substance so lit- 
