TET10LE, iii botmy, the slender stalk 
<hatsn.ppoi tsthekav.es of a plant. 
PE lTiV A, a genus of the class and order 
tetrandria. monogynia: the calyx is four- 
toothed, inferior ; corolla tour-parted, drupe 
with a two-celled nut. There is one species, 
a small tree of St. Domingo. 
PETP HO PRINCIPit, in logic, the tak- 
ing a thing for true, and drawing conclusions 
from it as such, \yhen it is really false, or at 
least wants- to be proved, before any inferences 
can be deduced trom it. 
PETITION. No petition to the king, or 
to either house of parliament, for any altera- 
tion in church or state, shall be signed by 
above twenty persons, unless the matter there- 
of is approved by three justices of the peace, 
or the major part of the grand jury in the 
country; and m London by the lord mayor, 
aldermen, and common council: nor shall 
•any petition be presented by more than ten 
persons at a time. 
Petition in Chancery, a request in 
writing, directed to the lord chancellor or 
master of the rolls, shewing some matter or 
cause, whereupon the petitioner prays some- 
what to be granted him. 
PETIVER1A, a genus of the tetragynia 
order, in the hexandrfa class of plants, and in 
the natural method ranking under the lath 
order, holoraceae. The calyx is tetraphyl- 
luus ; there is no corolla; and but one seed, 
with reflexed awns at the top. There are 
two species (Guinea hen-weed), herbs of the 
West Indies. 
PETREA, in botany, a genus of the didyna- 
rnia angiosperima class ot plants, with a mo- 
nopetalous flower, divided into five rounded 
segments at the limb. There is one species, 
a shrub of South America. 
PETRIFACTION, in natural history, de- 
notes the conversion of wood, bones, and 
other substances, principally animal or vege- 
table, into stone. These bodies are more or 
less altered from their original state, accord- 
ing to the different substances they have lain 
buried among in the earth; some of them 
having suffered very little change, and others 
being so highly impregnated with crystalline, 
sparry, pyritical, or other extraneous matter, 
as to appear mere masses of stone, or lumps 
-of the matter of the common pyrites; but 
they are generally of the external dimensions, 
and retain move or less of the internal figure, 
of the bodies into the pores of w hich this mat- 
ter has made its way. The animal substances 
thus found petrified' are chiefly sea-shells ; the 
teeth, bony palates, and bones of fish ; the 
bones of" End-animals, kc. These are found 
variously altered, by the insinuation of stony 
and mineral matter into their pores; and the 
substance of some of them is found to be 
wholly gone, there being only stony, sparry, 
or other remaining matter deposited in the 
shape and form of the original matter, which 
lias gradually wasted away, and these may be 
regarded as the true petrifactions. 
Respecting the manner in which petri- 
faction is accomplished, we know bat Lttle. 
It lias been thought by many philosophers, 
that this was one of the rare processes of na- 
ture'; and accordingly such places as have 
afforded a vie . of it, have been looked upon 
as great curiosities. However, it is now dis- 
covered, that petrifaction is exceedingly 
common; ami that every kind of water car- 
ries with it some earthy particles, which be-. 
Vox,, II. 
FETtllFACf tON. ^ 
ing precipitated from it, become stone of V 
greater or lesser degree of jiardness; and 
this quality is most remarkable • in those wa- 
ters which are much impregnated with sele- 
netic matter. Of late, it lias also been 
found by some observations on a petrifaction 
in East ’Lothian in Scotland, that iron contri- 
butes greatly to the process: and this it may 
do by its precipitation of any aluminous earth 
which happens to be dissolved in the water by 
means of an acid; for iron has the property of 
precipitating this earth, though it cannot pre- 
cipitate the calcareous kind. The calcare- 
ous kinds of earth, however, by being soluble 
in water without any acid, must contribute 
very much to the process of petrifaction, as 
they are capable of a great degree of hard- 
ness by means only of being joined with car- 
bonic acid, on which depends the solidity of 
our common cement or mortar used in 
building houses. 
The name petrifaction belongs only, as we 
have seen, to bodies of vegetable or animal 
origin; and in order to determine their class 
and genus, or even species, it is necessary 
that their texture, their primitive form, and 
in some measure their organization, are still 
discernible. Thus we ought not to place the 
stony kernels moulded in the cavity of some 
shell, or other organized body, in the rank of 
petrifactions properly so called. 
Petrifactions of the vegetable kingdom are 
almost all either gravelly or siliceous; and 
are found in gulieys, trenches, &c. Those 
which strike tire with steel are principally 
found in sandy fissures; those which effer- 
vesce in acids are generally of animal origin, 
and are found in the horizontal beds of calca- 
reous earth, and sometimes in beds of clay or 
gravel; in which case the ‘nature of the pe- 
trifaction is different. As to the substances 
which, are found in gypsum, they seldom 
undergo any alteration, either with respect to 
figure or composition, and they are very 
rare. 
A petrified substance, strictly speaking, 
is nothing more than the skeleton, or perhaps 
image, of a body which has once had life, 
either animal or vegetable, combined with 
some mineral. Thus petrified wood is no 
longer wood, properly speaking. When 
wood is buried in certain places, lapidific llu- 
ids, extremely divided and sometimes colour- 
ed, insinuate themselves into its pores, and 
fill them up. These fluids are afterwards 
moulded and condensed. The solid part of 
the wood is decomposed and reduced into 
powder, which is expelled without the mass 
by aqueous filtrations. In this manner, the 
places which were, formerly occupied by the 
wood are now left empty in the form of pores. 
This operation of nature produces no appa- 
rent difference either of the size or of the 
shape; but it occasions, both at the surface 
and in the inside, a change of substance, and 
tiie ligneous texture is inverted; that is to 
sav, that which was pore in the natural wood, 
becomes solid in that which is petrified ; and 
that which was solid or full in the first state, 
becomes porous in the second. In this way, 
says M. Musard, petrified wood is much less 
extended in pores than solid parts, and at the 
same time forms a body much more dense and 
heavy than the first. As the pores communi- 
cate from the circumference to the centre, 
the petrifaction ought to begin at the centre, 
and end with the circumference of the organ- 
365 ’ 
ic body subjected to the action of the Tapi 
dific fluids. 
In proportion to the tenderness and bad 
quality of wood, it imbibes the greater quail-’ 
tity of water ; therefore this sort will unques- 
tionably petrify more easily than that which 
is hard. It is thought that all the petrified 
wood so often found in Hungary, has been' 
originally soft, such as firs or poplars. Sup- 
pose a piece of wood buried in the earth ; if 
it is very dry, it will suck up the moisture 
which surrounds it like a spurige. This 
moisture, by penetrating it, will dilate all the 
parts of which it is composed. The trachke, 
or air-vessels, will be filled first; and then the 
lymphatic vessels, and those, which contain 
.the succus proprius, as they are likewise 
empty. The water which forms this moisture 
keeps in solution a greater or a less quantity 
of earth; and this earth, detached, and car- 
ried along in its course, is reduced to such an 
attenuated state, that it escapes our eyes, 
and keeps itself suspended, whether by the 
medium of fixed air or by the motion of the 
water. Such is the lapidific fluid. Upon 
evaporation, or the departure of the men- 
struum, this earth, sand, or metal, again ap- 
pears in the form of precipitate or sediment in 
the cavities of the vessels, which by degrees 
are filled with it. This earth is there mould- 
ed with exactness: the lapse of time, the- 
simultaneous and partial attraction ot the 
particles, make them adhere to one another; 
the lateral suction of the surrounding fibres, 
the obstruction of the moulds, and the liard- 
. ening of the moulded earth, become general ; 
and there consists nothing but an earthy sub- 
stance which prevents the sinking of the 
neighbouring parts. If the deposit is formed 
of a matter in general pretty pure, it preserves 
a whiter and clearer colour than the rest of 
the wood ; and as the concentric layers are 
only perceptible and distinct in the wood, be- 
cause the vessels are there more apparent on 
account of their size, the little earthy cylin- 
ders, in the state of petrified wood, must be 
there a little larger, and consequently must re- 
present exactly the turnings and separations 
of these layers. At the place of the utriculi, 
globules are observed, of which the shapes 
are as various as the moulds wherein they are 
formed. The anastomoses of the proper and 
lymphatic vessels form, besides, points of 
support or reunion for this stony substance. • 
With regard to holes formed by worms in 
any bits of wood, before they had been bu- 
ried in the earth, the lapidific fluid, in pene- 
trating these great cavities, deposits there as 
easily the earthy' sediment, which is exactly' 
moulded in them. These vermiform cylin- 
ders are somewhat less in hulk than the holes 
in which they are found, which is owing to 
the retreat of the more refined earth, and to 
its drying up. 
Let any one represent to himself this col- 
lection of little cylinders, vertical, horizontal, 
inclined in different directions, ■ the stony 
masses of Utriculi and of anastomoses, and he 
will have an idea of the stony substance which 
forms the ground-work of petrifaction, Hi- 
therto not a single ligneous part is destroyed.; 
they are all existing, but'* surrounded on 
every side with earthy deposits; and that 
body which, during life, Was composed of so- 
lid and of empty parts, is now entirely solid; 
its destruction and decomposition do'- not 
take place till after the formation ol these Rule 
