§86 Mr. Hatchett’s Observations on the Change 
phosphate of lime ; the shells forming the lumachella of Bley- 
berg, which still possess the lustre and iridescence of their 
original nacre; and the shells found at Hordwell in Hamp- 
shire, and in Picardy, which are chiefly porcellaneous, but more 
or less calcined ; also the fossil echini and others, so commonly 
found in the limestone, chalk, and calcareous grit of this island, 
which, although they retain their original figure, are intirely, 
or at least externally, formed of calcareous spar, incrusting a 
nucleus of flint or chalcedony. And if, in addition to these, we 
may be allowed to regard the more recent limestone and chalk 
strata as having been principally or partly formed from the 
detritus of animal exuviae, we shall possess a complete series 
of gradations, commencing with animal substances analogous in 
properties to those which are recent, and terminating in bodies 
decidedly mineral, in which all vestiges of organization have 
been completely destroyed. 
The vegetable kingdom has likewise produced many instances 
not less remarkable; and it is worthy of notice, that animal 
petrifactions are commonly of a calcareous nature, while, on the 
contrary, the vegetable petrifactions are generally siliceous;* 
It is not, however, my intention here to enter into a minute 
discussion concerning the formation of these extraneous fossils ; 
I shall therefore proceed to consider other equally or perhaps 
more important changes, which organized bodies, especially 
vegetables, appear to have suffered, (after the extinction of the 
principle oflife,) by being long buried in earthy strata, and by 
being thus exposed to the effects of mineral agents. 
* Pyrites, ochraceous iron ore, and fahlertz, are also occasionally found in the forms 
[of vegetable bodies. 
