but as their direftion is always1 confiant, fo are the principal ’
elements côriiïantly the’fame in.each . ftratum, notwithftanding,
the Various difthnces o f 1 its parts.. The ftone which occupies
the higheft parts o f the ifland, as well near the Jake of Jefero,
aë about Lujin.pkciolo, is analogous to the common marble ofi
IJlria; ohly it contains a greater quantity o f marine bodies o ff
the moil diftrnguiihabie fpecies, and which ufually are better-
preferved than the’-others/ 1 ‘tn'ezn_ ph'acites and ' elicites-.-of- evcftt<
variety and fize. The quantity o f thefe bodies femipetrified, or.
changed into ftaladtites,. but not become of equal hardnefs with
the matricein which they are contained, renders that marble, lefs ,
ftrong, and lefs apt to relift the aftion o f the air, and corrofion,
than thé Iftrian, The iancient fea bottom, hardened by time,
and the operative faculty o f the waters uniting the particles moft
apt to' coin'crete in cryftals, has been . abundantly peopled .with
large an'd'ftnall nummali, and fragments o f them, many, ages before
it was expofed to the open air. Thefe adventitious bodies,
o f which the fpecies is juftly fuppofed to be loft, were probably
not fo eafily compreflible as other fofter'and. unconnected
parts o f the mud-,‘ i hence it would follow, that, preferving
fome degree of their difpofition towards calcination, they were
ihut up in the petrifaction of large ftrata. Whenever it happens
that they are expofedto the violent aftion of. any exterior force,
they foôn begin fo be difeompofed, in fuch a manner, that the
fuperftcies o f a piece o f this ftone, which is almoft half
'compofed o f them, fliews manifeftly its difpofition to be dif-
united, reduced into powder, and confirmed by time. Not--
wrthftanding, however, this fmaller degree, of hardnefs which
the nummali have when inclofed in the ftrata that compofe the.
tops o f the mountains o f the ifland, they ufe, when entire, to
refill time and corrofion better than the reft o f the ftone, in con--
fequence.
fequence o f their ftrufture, which, between the lamina, left room
for a fparry cryftallization. Hence the nummali and frumenta-
rie o i Cherfo, remain confiderably. prominent, and lefs worn than
the ftone in which they Tie, though .they are,.evidently not f o -
hard; w.hich is, a proof that the. greater or leffe-r folidity and apparent
comp aft nets o f a body, is not a fure rule o f proportion
to determine the durability, . which,rather dqpqnds on the fecret -
nature,and difpofition o f the particles whereof it is, compofed, -
and the fpecies o f force aftuatjng towards it deftruftipn. Arid -
though the caufe does not appear outwardly, .the larpe thing is -
frequently feen in. various.kinds cfffoliil,matter,„and. the extraneous
body, ..though fpecificaily lefs compaft, .refills longer than.
the. marble, • ox-feftflusfvp. which it is. contained.. The fmall
differences of the combination o f the elements,, which concurred'
to form any portion of a ftratum, and the very minute varieties
o f fituation, air, earth, water, and effluvia,. not, reducible to-
calculation,, are altogether, or taken feparately, the caufes o f
the moft remarkable differences between hones, which, however,
have all the fame bafis, . Mineral, fubftances when diffolved.
tinge the earth, o f which the haudeft marble is formed, o f various,
colours, in.proportion to their quality: and quantity ; and
it happens, not unfreqiiently, that, marble ftrata, already . hardened,
through the intervention- oft water or fire, .imbibe, or
■ open their pores to let in a colouring matter, or mineral efflu-
vium, which changes their fecondary qualities almoft radically.
Hence, taking the whole lithological kingdom together, it may .
freely be afferted, that, the waters charged with heterogeneous
particles, and the fubterr mean vapours, have almoft as confide-
rable a part in the alterations o f the combination o f ftones,. as
the .vulcanic fires, which melt, reduce to aihes, .and mix with
an infinite variety, the fubftances varioufly combined, on which
they