B A S A 
ther in Hoping directions. They are alfo generally fepa- 
rated a little from one another when they are regular. The 
nature of the thing requires this, becaufe the feveral par¬ 
ticle’s of which the cry Hals are compofed muft have the 
liberty of obeying that power which affects their conftitu- 
tion. The bafaltic columns, on the contrary, whole height 
is frequently from thirty to forty feet, are placed parallel 
to one another in confiderable numbers, and fo clofe toge¬ 
ther that the point of a knife can hardly be introduced 
between them. Befides, in moll places, each pillar is di¬ 
vided into feveral parts or joints, which feem to be placed 
on one another. And indeed it is not uncommon for cryf- 
tals to be formed above one another in different layers, 
while the folvent has been vilibly diminiflied at different 
times: but then the upper cryftals never fit fo exactly up¬ 
on one another as to produce connected prifms of the fame 
length or depth in all the llrata taken together; .but each 
ftratum, feparately taken, produces its own cryftals. Pre¬ 
cipitation, both in tlie wet and dry way, requires that the 
particles fliould be free enough to arrange themfelves in a 
certain order; and, as this is not practicable in a large 
melted mafs, no cryftallizations appear, except on its fur- 
face or in its cavities. Add to this, that the bafaltes in a 
frefti fratlure do not Ihew a plain fmooth furface under 
the microl'cope; but appear fometimes like grains of dif¬ 
ferent magnitude, and at other times referable fine rays 
running in different directions, which does not correfpond 
with the internal ftruCture of cryftals. Hence the opinion 
of bafaltes being formed by cryftallization either in the wet. 
or dry method muft become lets probable; but it muft not 
be omitted, that the fpars exhibit a kind of cryftallization, 
which at firft fight refembles a heap of bafaltes, but upon 
a clofer examination a very great difference is to be found. 
The form of the fpar is every where alike, but the bafal¬ 
tes differ from one another in fize and the number of tides. 
The former, when broken, confifts of many fmall unequal 
cubes; but the bafalt does not feparate in regular parts. 
“Nature’s f'econd method of producing regular forms is 
that of eroding the outer furface of a melted mafs. By 
a fudden refrigeration, nature, to effeft this purpofe, makes 
ufe of polyhedrons and irregular forms. If we fuppofe a 
confiderable bed which is made fluid by fire, and l’pread 
over a plain, it evidently appears that the furface muft 
firft of all lofe the degree of heat reqnifite for melting, 
and begin to congeal. But the cold reqnifite for this pur¬ 
pofe likewife contracts the uppermoft congealed ftratum in¬ 
to a narrower fpace; and confequently caufes it to fepa¬ 
rate from the remaining liquid mafs, as the fide expofed 
to the air is already too ftiff to give way. Ia this man¬ 
ner a ftratum is produced, running in a parallel direction 
with the whole mafs; others are (till produced by the fame 
caufe in proportion as the refrigeration penetrates deeper. 
Hence we may very plainly fee how a bed may be divided 
into ftrata. In the fame manner the refrigeration advan¬ 
ces on the fides; which confequently divides the ftratain- 
ta into polyhedrons pillars, which can hardly ever be ex¬ 
actly fquare, as the ftrongeft refrigeration into the inner 
parts of the mafs advances almoft in a diagonal line from 
the corners. If we add to this, that a large mafs cannot 
be equal through its compofition, nor every where liquid 
in the fame degree, it will be eafy to difeover the caufe of 
feveral irregularities. If the depth of the bed be very 
confiderable in proportion to its breadth, prifmatic pillars 
without crofs divifions will be formed at leaft lengthwile 
from the uppermoft furface downwards. 
“ The third way is perfectly fimilar to the preceding in 
its effeCt; but it is different from it by the mafs being foak- 
ed in water, and by the burfting of it afunder, being the 
effeCt of the contraction while it is drying. If we fuppofe 
Inch a bed to be fpread over a level fpace, the drying ad¬ 
vances in the fame manner as the refrigeration in the for¬ 
mer cafe. This ieparation into ftrata properly happens 
when a confiderable quantity of clay enters into the whole 
compofition, becaufe the clay decreafes more than any 
ether kind of earth in drying. It is mod probable there* 
L T E S. x 771 
fore, that the pillars have been produced out of the ba¬ 
faltic fubftance while it was yet foft, or at leaft not’too 
hard to befoftened by exhalations. If we therefore fup. 
pofe a bed to be fpread over a place where a volcano be¬ 
gins to work, it is evident that a great quantity of the wa¬ 
ter always prefent on fuch occafions muft be driven up¬ 
wards in exhalations or vapours; which, it is well known, 
poffefs a penetrating foftening power, by means of which 
they produce their firft effeCt: but, when they are increa- 
fed to a fufficient quantity, they force this tough moift 
fubftance upwards; which then gradually falls, and du¬ 
ring this time burfts in the manner above-deferibed.” 
Mr. Kirwan is alfo of opinion, that the bafaltes owe 
their origin both to fire and water; they feem to have 
been at firft a lava ; but this, while immerfed in water, 
was fo diffufedand diffolved in it with the affiftance of heat, 
as to cryftallize when cold, or coalefce into regular forms. 
That bafaltes is not the etfeCt of mere fufion he concludes 
from comparing its form with its texture. Its form, if 
produced by fufion, ought to be the effeCt of having flow¬ 
ed very thin ; but in that cafe its texture (hould be glaffy : 
whereas it is merely earthy and devoid of cavities. Hence 
we may underftand how it comes to pafs tliat lava perfect¬ 
ly vitrified, and even water, have been found inclofed in 
bafaltes. 
M, Houel, in his Voyage PiElurefque, is at confiderable 
pains to account for the origin of the different fpecies of 
bafaltes he met with in the neighbourhood of Etna. 
“ Some modern writers (fays he) attribute the configura¬ 
tion of the bafaltes to the fudden cooling of the lava in 
confequence of the effeCts produced upon it by the cold- 
nefs of fea-water, when it reaches the fea in a Hate of fu¬ 
fion. They fuppofe that the fhock, which it then re¬ 
ceives, is the caufe of thofe different configurations which 
this fubftance aftumes; the mod remarkable of which have 
been already mentioned. This affertion, however, feems 
to be ill founded. By confidering the bafaltic rock repre- 
fented in the Plate, we find that the pile is not in its ori¬ 
ginal ftate, and that the feries of columns is at prefent in¬ 
complete. It is very probable, that the fpecies of clay 
found there, and which is extraneous to the bafaltes, has 
by feme means taken poffeflion of its place ; and it like¬ 
wife appears, that not one of the bafaltes here deferibed 
is entire. It feems incredible, however, that a mafs of 
matter reduced by fire to a ftate of ljquefaCtion, and flow¬ 
ing into the fea, (hould be fuddenly changed into regular 
figures by the (hock of coming into contact with cold wa¬ 
ter; and that all the figures which are thus formed (hould 
be difpofed in the fame manner with regard to one ano¬ 
ther. For, if we fuppofe that the water made its way in¬ 
to the cavity of the lava at the inftant when it retreated 
backwards, then might the lame quantity of water pene¬ 
trate into the mod remote parts of the mafs; and by that 
means prolong the cavity which it had begun to form when 
it firft entered the mafs. The water then being lodged 
within this burning maff, and being in a ftate of dilata¬ 
tion, would have expelled whatever oppoled it, and fwell- 
ed the whole mafs in fuch a manner as to form much lar¬ 
ger interftices than thofe which appear between the bafal- 
tic columns; fince thefe are every where in clofe contact 
with one another. Befides, how could the fudden cooling 
of the lava divide the upper part and (ides of fuch an' 
enormous mafs as exactly as if they had been caft in a mould 
made on purpofe ? 
“ It remains alfo for thofe who adopt the hypothefis in 
queftion to explain how the fhock occafioned by the cold 
water (hould make itfelf felt beyond a certain depth ; fince 
the very firft moment it comes into contaCl with the li¬ 
quid lava it muft ceafe to be cold 5 for the lava cannot but 
communicate to it a greater degree of heat than tt com¬ 
municates of cold in return, as the water is more ea(ily 
penetrable by the burning lava than the mafs of lava by 
the furrounding wafer. But farther, if at the firft mo¬ 
ment after the lava enters the water it were cooled and 
contracted, the water would foon prevent, by the contrac¬ 
tion 
