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served. In other cases the minute fibres and tubes of the animal are 
not expressed by the silex which has filled the spaces which they 
occupied, yet the external form represents with faithful accuracy that 
of the body which afforded to the silex its mould or nucleus. 
“‘ Before the consolidation of the original compound fluid, which is 
now hardened and separated into beds and nodules of flint and chalk, 
a variety of organic bodies being dispersed through its mass would 
afford a number of nuclei, to which, in separating itself from the chalk, 
the silex seems to have had a tendency to attach itself. Hence the 
insulated nodules that occur irregularly in the chalk, out of the line of 
the flinty strata, do, I believe, bear traces of an organic nucleus ; so 
also in many cases do those that occupy the flinty strata. But the 
greater number of these latter, though their form be usually that of 
nodules separated from each other by an intervening portion of chalk, 
yet indicate no traces that refer them to organic origin, and are some- 
times extended into thin, continuous tabular masses. 
“The organic bodies that afforded nuclei to these nascent flints 
appear to have been dispersed pretty uniformly through the original 
compound mass, which is now divided into beds of chalk and flints ; 
but it is not easy to determine what cause it was that regulated the 
distances at which the beds of flints have been disposed, or to say why 
we sometimes find organic bodies preserved in flint, at other times 
enveloped and filled by pure chalk. The solution of the latter ques- 
tion may be, that different genera of organic remains afforded centres 
that attracted the silex with unequal force, and that this will in some 
degree explain the phenomenon so common in the Chalk formation, 
that bodies allied to the genus Sponge and Alcyonium are most fre- 
quently preserved in flint and calcedony, whilst shells and other 
bodies, which in their natural state were more calcareous, generally 
have their form retained by chalk or calcareous spar.” 
There are no organic remains discovered in the substance of the 
