And the “ Great Carolina Marl Bed.” 37 
(though this will have its bearing on the result,) as 
upon that of the mineral solutions which percolate 
the earth, the fossils being calcareous, silicious, ferru- 
ginous, and the like, according as the water contains 
lime, flint, or iron, etc. In all cases, the process seems 
to be essentially the same; a gradual decay and 
dissipation of the organic atoms, and a gradual sub- 
stitution, through permeation, of the mineral or inor- 
ganic. 
“Tn many cases the fossil itself is petrified anew, so 
to speak ; that is, the mineral matter which was at first 
deposited, is gradually dissolved out, and a new sub- 
stance takes its place; or no new matter may be sub- 
stituted, and merely the hollow mould be left to 
prove that the organism was once there. Thus a 
shell or a coral which consist of organized carbonate 
of lime may be converted into the sparry mineral 
carbonate; and this may be dissolved and washed 
away, leaving a hollow mould marked with every 
ridge and line of the vanished organism; or this 
mould may be filled up again with silicious matter, 
so that the shell or coral seems to have been trans- 
muted into flint, without losing the most delicate line 
traced on its original surface. The perfection with 
which the finest lineaments are thus preserved, after 
every particle of matter in the fossil has been twice 
changed, is almost incredible. 
“ Of course all plants and animals are not preserved 
alike, nor are the same organisms always found in the 
same state of preservation. Those that have partially 
decayed in the air before being imbedded in the earth 
