[ 39 8 ] 
place, they will remain fair and /harp, fuffering very 
little change by any length of time ; whilfl the flefh 
of thefe, being fubje<5t to putrifa&ion, is foon deftroy- 
ed ; and yet, according to circumftances that happen, 
fome of thefe may be replaced in due form by itony 
particles. 1 have a gryphites, with the form of the 
h/h in its place, as is the cafe in feveral of the oyfter 
kinds. This may be occaiioned by the /hells being 
clofe, or nearly fo, and ftony matter gradually infinu- 
ating into their cavity, fo as to fill up the whole. 
Wood. 
The kinds of wood found foffil are very different: 
fome are of a firmer texture than others : and this too 
is according to the places wherein they are depofited. 
Some I have feen fo highly impregnated with a fine 
itony and pyritical matter, as to bear a polifh like a 
pebble ; fome, tho’ quite reduced to done, yet pre- 
serving the fibrous appearance of the original /late 
and fome which is found in boggy bottoms, being not 
at all changed, except in color : this is called bog oak, 
or bog deal, well known to country people in many 
places of thefe three kingdoms, who light themfelves 
about their bufinefs with flips of this wood, cut on 
purpofe inftead of candles, as it burns with a clear and 
durable flame. It is remarkable, that altho’ oak or 
fir /hall lie ages immerfed in water under ground, it 
fhall not putrify 5 but acquire fuch fulphureous par- 
ticles by lying in fleep, in the bog- water, as to qua- 
lify it for this ufe. Other wood, depofited in marly 
ground, is found incrufled over, trunk and branches, 
with a white cruft ; the wood remaining intirc within. 
At 
