liquid mafs whilil it is cooling : and,
3dly, the burfting o f a moiil fubftance
whilil it is drying.
The firil method is the moil common,
but to all appearance nature has
not made ufe o f this in the prefent
.cafe. Cryftals are feldom or never
found in any coniiderable quantity
running in the fame diredion, but
either inclining from one another, or,
what is ftill more common, placed towards
one another in feveral iloping
diredlons. They are alfo generally
feparated a little from one another,
when they are regular; the nature o f
the thing likewife requires this; becaufe
the feveral particles, o f which the cryftals
are compofed, niuft have the liberty
o f following that power which
arfeds their regular difpoiition.
The bafalt columns, on the contrary^
whofe height are frequently from thirty
to forty feet, are placed parallel to one
another in coniiderable numbers, and
fo clofe together that the point o f a
knife can hardly be introduced between
them. Beiides, in moft places,
each pillar is divided into feveral
parts
parts or joints, that feem to be placed
upon one another; and indeed it is
not uncommon for cryftals to be
formed above one another in dilFerent
layers, when the folvent has been
viiibly diminiftied at cliiFereiit times ;
but then the upper cryftals never fit
ib exadly upon the lower ones as to
produce conneded prifms of the fame
length and depth as all the ftrata taken
together, but each ftratum feparately
forms its own cryftals.
How then can the Giant’s Caufe-
way, in the county o f Antrim, Fingal’s
Cave at Staffa, and all other affem-
blages o f pillars o f the fame kind, be
confidered as cryftallizations ? Precipitation,
both in the wet and dry
manner, requires that the particles
ihould be free enough to fix themfelves
in a certain order ; and as this
is not pradicable in a large melted
inafs, no cryftallizations appear in it,
except on its furface, or in its cavities«
Add to this, that the bafalts in a
frefli fradure cio not ihew a plain
fmooth iiirfacc under die microfcope,
but appear fometimes like grainS" of
ercnt magnitude, and at other
time