518 Petrifactions. MIN E R A L Q G Y. Petrifactions.' 
removed, and its place fupplied by tlie depofition of frefli 
earthy matter: feldom however entirely; for, in making 
a tranfverfe fedlion of any of the branches of fuch a mafs, 
there may be generally oblerved the trace of a longitu¬ 
dinal cylindrical cavity; which fhows that the deposition 
originally took place on fomething that has been fubfe- 
quently removed. The incipient ffage of the procefs juft 
defcribed, may be feen in fome of the fprings of Shot- 
over-hill, near Oxford : and in many of the fmall brooks 
which run into the Cherwell on the north lide of that 
city. The dead leaves, &c. found in the bottom of thefe 
brooks,'being generally covered with a thin earthy in- 
cruftation, which readily peels off. 
Mr. Parkinfon, in the firft volume of his valuable work 
on the Organic Remains of a Former World, attempts to 
fhow that the generally-received opinion refpecting the 
formation of petrifactions is erroneous. He fupports his 
conjectures by a particular examination of various vege¬ 
table foffils. It has been fuppofed, that, in every inftance 
of petrifadlion, the lapideous is lubftituted for the vege¬ 
table or animal matter, as this is decompoled and re¬ 
moved. This removal and fubffitution has been all'oFup- 
pofed to be lb gradually performed, molecule by mole¬ 
cule, as to allow the earthy parts, vvhillt arranging them- 
l'elves in the fpaces left by the removal of the organized 
matter, fo to mould themfelves in thole fpaces, as to take 
exadfly the form of the organized part, and to imitate it 
precifely in every trace. In this manner the petrifadlion, 
as it is termed, is fuppofed to have acquired the exadl 
form, and moll of the charadteriftic appearances, of the 
original body, without retaining any at all of its original 
particles. This mode of explaining the formation of pe- 
.trifadlions has been adopted by almoft every chemifl and 
mineralogift who has written on the fubjedl; and has 
been particularly defcribed by Kirwan, Walch, Dauben- 
ten, Fourcroy, and Haiiy ; the latter gentleman giving it 
as the explanation which is moll generally admitted, al¬ 
though he acknowledges that it may not be free from 
difficulties. 
Diffatisfied with this explanation, Mr. Parkinfon fug- 
geHs that the organized part was not removed ; but that 
it remained in part, at lead, and became the fubllratum of 
the folfil on which was depofited the lapidifying matter. 
He endeavours to fhow that vegetable fubllances, in cer¬ 
tain iituations, were rendered bituminous ; and were, in 
that Hate, capable of being thoroughly pervaded by water, 
and, of courle, of being imbued with the faturated folu- 
tion of any earth ; and that, by the formation of minute 
cryllallizations through the whole impregnated mafs, a 
confolidated iiliceous or calcareous fubltance could be 
formed, without dillurbing the exilling arrangement of 
thole parts on which the form and general appearance of 
the foil'll would depend. To determine how far this opi¬ 
nion was correCt, wood petrified by flint, was fubje&ed to 
Ample diltillation over a naked fire, when an oily fubli- 
mated film, pofleffing a llrong empyreumatic fmell, was 
obtained. It could not be expe&ed, from the refraftory 
nature of Alex, that any thing more decifive could be ob¬ 
tained from any experiment on opaline wood ; Ance no 
agent could, perhaps, be employed for the removal of the 
earth, which would not at the fame time entirely decom- 
pole the bituminous fubllratum. But in calcareous foil'd 
wood this objection did not exifl, Ance, by the employ¬ 
ment of any dilute acid, the earth might be removed, and 
it might be clearly afcertained whether the prefumed ve¬ 
getable or bituminous matter was prefent or not. The 
experiment was made, and with complete luccefs : the 
carbonat of lime was removed by diluted muriatic acid, 
and a dark-brown, friable, but coherent, mafs remained, 
which bore every appearance of bituminous wood, and 
which, when brought into contact with the flame of a 
candle, direCtly burned with a fmall, bright, lambent, 
flame, and yielded a llrong bituminous odour. 
From this experiment, Mr. Parkinfon conceived him- 
felf warranted in concluding that, with refpeCl to vege¬ 
tables, the procefs of petrifadlion is not merely, as Mr. 
Kirwan luppofes, the fubftitution of Itony or metallic bo¬ 
dies in the place of the organic fubltance which has been 
deltroyed by putrefaction ; nor, as is taught by Fourcroy, 
that the petrifying matter is depofited as in a mould ; the 
complete deltru&ion of the vegetable matter, and the dif- 
appearance of whatever conllituted its elements, taking 
place at the lame time; but that a part of the organic- 
matter Hill remained, though fomewhat changed; and 
that the procefs of petrifadlion was the impregnation of 
this fubltance, and the filling up of the interffices, with 
the lapidifying matter. 
It fall remained to determine if a correfpondent orga¬ 
nic matter exilted in animal foffils. To afeertain this 
point, therefore, various kinds of animal .foffils were fub- 
jedted to a .chemical examination, by which the moll fa- 
tisfadlory proofs were obtained of the exiltence of this 
animal matter, and even of its retaining, in feveral in- 
Itances, very much of its original form. This circum- 
llance was beautifully illullrated by the examination of 
an entrochus of the lily encrinite. A fimilar examina¬ 
tion of the foffil tubipore, was equally fuccefsful; the 
animal membrane belonging to the coral, from which the 
marble derived its origin, being rendered exceedingly 
evident. In a fubfequent examination of this marble, 
the animal membrane was difplayed, retaining the gene¬ 
ral external form, with the original colour of the coral. 
The experiments were performed fuccefsfully with feve¬ 
ral other fubllances ; particularly with a piece of the Der- 
byfliire entrochal marble, the animal membrane of which 
was rendered perfedlly dillindl. 
Other experiments have convinced Mr. Parkinfon, that 
the prefence of organic matter in animal foffils, of almoil 
every kind, is fufficiently frequent to authorife, in the 
full ell manner, the opinion which he has advanced, re- 
Ipedling the principles on which the procefs of petrifac¬ 
tion is accompliihed. In the vegetable foffils, it is true 
that the organic matter appears to have undergone a par¬ 
ticular change, having been previoully brought to the 
Hate of bitumen ; and Mr. Parkinfon has llrong reafons, 
the rel'ult of adlual obfervation, for believing that, in the 
animal foffils, a correfpondent change has been previoully 
induced, and that the animal matter has fuffered a con- 
verfion into adipocire. 
Before we treat of the genera, in the order in which 
they Hand, we lhall give a few extradls from Mr. William 
Martin’s “Attempt to .gHablilh a Knowledge of extra¬ 
neous Foffils on fcientific Principles.” 
Foffils are ufually dillinguiffied into furtive and extraneous. 
Native foffils, or minerals, are foffils dellitute of an or¬ 
ganic form, exhibiting fuch a HruCture only as arifes from 
the appolition or continual addition of the particles of 
which they are compofed. Extraneous foffils, or reliquia , 
relics, are foffils that have the form or Hructure of animal 
or vegetable bodies. Extraneous foffils comprehend two 
lorts of animal and vegetable relics, viz. the confervata 
and pet r if ad a : the former are the remains of animals or 
vegetables, preferved by various operations of nature 
among minerals; the latter are mineral bodies, which 
have received their form from animals or vegetables. 
Extraneous foffils have been found in every quarter of 
the knowm world. They are met with embodied in the 
hard rocks and Hones ; but they are not equally common 
to all rocks and mineral fubflances, inafmuch as granite, 
Aenite, gneifs, micaceous l’chiflus, and fome fpecies of 
limeffone, never contain organic remains; and thole 
rocks, in which extraneous foffils are never found, con- 
llitute the highelt mountains. The parts of organized 
bodies moll common in a loffil Hate, are thofe which are 
known longed to reAH putrefadlion and decay: thefe are 
wood, and the leaves and Hems of certain plants ; Ihells, 
bones, corals, and other hard parts of animals. Very 
tender and fucculent bodies, whether animal or vegetable, 
are rarely found in a foffilized Hate. Shells, and various 
exuviaa of the vermes clafs, are molt commonly found in 
the 
