£78 LA 
year 1329, on which foil had accumulated to the depth of 
eight inches; while on the other hand Spallanzani men¬ 
tions a lava which rufhed into the lea in the year 1320, 
but ftill preferves in every part its hardnels and fterility. 
Thole lavas which are the lighted: and lead: vitrified, and 
at the fame time contain the greateft proportion ot alu- 
mine and oxyd of iron, are the molt eafily dilintegrated ; 
and, where the proportions of the conftituent parts of a 
dilintegrated lava are fuch as to he capable of retaining 
a juft portion of moifture for the longeft time, the fertility 
of the refulting foil is greateft. Nothing can be more fer¬ 
tile than the fields of Catanea, and all the bafe of Etna. 
But volcanic eruptions do not invariably produce lava : 
the volcanoes of Quito, the flames of which are fometimes 
elevated three thoufand feet, have never produced a fingje 
drop of running lava. They fend forth water, inflamma¬ 
ble air, dirt, and clay impregnated with coaly' matter. 
Similar muddy eruptions occafionally take place in other 
volcanoes alfo. 
The quantity of matter thrown out from volcanoes un¬ 
der the name of lava is prodigious. After the great erup¬ 
tion of Etna in 1669, Borelli went from Pifa to Sicily to 
obferve the effects of it. The matter thrown out at that 
time amounted to 93,830,750 cubical paces; fo that, had 
it been extended in length upon the furface of the earth, 
it would have reached more than four times round the 
whole globe. All this matter, however, was not lava, but 
conlifted alfo of fand, ftone, gravel, &c. The lava he 
computed at 6,300,000 paces, which formed a liver, ac¬ 
cording to our author fometimes two miles broad ; but 
according to others it was fix or feven miles broad, and 
lometirnes twenty or thirty yards in depth. Sir William 
Hamilton informs us, that the Lavas of Etna are very 
commonly fifteen or twenty miles in length, fix or feven 
in breadth, and fifty feet deep : the moll confiderable 
are fcarcely lefs than thirty miles long and fifteen broad. 
The mod confiderable lavas of Vefuvius do not exceed fe¬ 
ven miles in length. The fame author, however, tells us, 
that the lava which ilfued from Vefuvius in 1767, was fix 
jniles long, two in breadth, and in molt places fixty or fe- 
venty feet deep. In one place it had run along a hollow 
way made by currents of rain not lefs than two hundred 
feet deep and one hundred wide; and this vaft hollow it 
had in one place filled up. He fays, he could not have 
believed that fo great a quantity of matter could have been 
thrown out in fuch a ftiort time, if he had not examined 
the whole conrfe of it himfelf. Even this quantity, how¬ 
ever, great as it is, appears very trifling in comparifon to 
that thrown out in Iceland in the year 1 783, which covered 
a fpace of ground ninety miles in length and forty-two in 
breadth, to the depth of more than a hundred feet. Dr. 
VanTroil, in his Letters on Iceland, tells us, that he and 
his companions travelled over a trait of lava upwards of 
three hundred miles in length ; and in 1728, we are told 
that an eruption of lava took place, which continued for 
two years to run into a great lake, which it almolt filled 
lip. See Iceland, vol. x. p. 728. 
Sir William Hamilton informs 11s of a curious faft re¬ 
lating to a lava in the ifland called Lacco. Here is a ca¬ 
vern (hut up with a door; and this cavern is made ufe of 
to cool liquors and fruit, which it does in a fhort time as 
effectually as ice. Before the door was opened, he felt 
the cold on his legs very feniibly ; but, when it was open¬ 
ed, the cold rufhed out fo as to give him pain; and within 
the gikrtto it was intolerable. He was not fenfible of 
wind attending this cold; though upon Mount Etna and 
Vefuvius, where there are caverns of this kind, the cold 
is evidently occafioned by a fubterraneous wind : the na¬ 
tives call fuch places ventaroli. From old lavas there alfo 
frequently happens an eruption of noxious vapours called 
■mojetes. Tbefe likewife break out from wells and fubter- 
raueous places in the neighbourhood of a volcano before 
an. eruption. Our author tells us, that the vapour affects 
the noftrils, threat, and ftomach, juft as the fpirit of hartf- 
horn or any ftrong volatile fait; and would loon prove 
y a. 
fatal if you did not immediately withdraw from it. Thefts 
mofetes, he fays, are at all times to be met with under the 
ancient lavas of Vefuvius, particularly the great eruption 
ol 1631. 
Some kinds of lava take ^a fine pollfh, and are frequently 
manufactured into boxes, tables, &c. In Naples, the in¬ 
habitants commonly make life of it for paving the ftreets ; 
and even the fubterraneous cities of Pompeii and Hercula¬ 
neum have been paved with the fame fubftance. The lava 
of Etna appears to be ftill more generally ufed for build¬ 
ing, fince, according to Ferrari, there is net a houie in its 
neighbourhood that is not conltructed of it. The rapid 
progrefs in the rebuilding of Catanea (!ee vol. iii. p. 899) 
was in a great-meafure owing to the facility with which 
the building-materials were procured. Alfo mill-ftones 
are made of the lava of Etna, many of which are exported 
to Calabria and Malta; and it has even been manufactured 
into canon balls. A fine large cubic piece of lava is pre- 
ferved in the hall of the Britifn Mufeum. 
Species. 1. Lava compachi, or com pa ft lava. Specific 
character, nearly opske, compact, hardifh, of a conchoidal 
texture. Found in volcanic mountains and their neigh¬ 
bourhood, appearing to have been fufed by the aftion of 
fire, but not vitrified, and becoming, when cooled, com¬ 
pact, clofe, and lolid, and bearing the refemblance of its 
original mineral. Colour generally blackifii, fometimes 
grey, brown, or red, rarely white, very rarely .green or 
blue; its fubftance is fo very little porous as to admit be¬ 
ing cut into flabs with an almoft entire furface, and po- 
lifhed like marble; fracture earthy or fine fplintery, more 
rarely foliated. Contains often hornblende, white garnet, 
olivin, calcareous fpar, mica, fnorl, See. 
2. Lava vitrea, or vitreous lava : diaphanous, (Lining, 
compact, hard, of a conchoidal texture, Found abouc 
volcanic mountains in New Spain, Peru, Hecla, Vefuvius, 
and fometimes in places where fubterraneous fires have 
taken place either from pyrites or in coal-pits ; contains 
generally other fubftances imbedded, and is more or lefs 
tranfparent; colour generally black, rarely cinereous, 
greenifii, bluifti, or white, fometimes priftnatic ; ufually 
of a common, rarely of a ftalaftitical, globular, or pyra¬ 
midal, form ; melts with more difficulty than other lpe- 
cies, on account of its containing lefs iron, carbonat of 
lime, and magnefia; is frequently Jo hard as to ftrike fire 
with fteel. 
The lava, at its firft difeharge from the crater of a vol¬ 
cano, is in a ftate of prodigious ignition, greatly fuperior 
to any thing we can have an idea of from the (mail arti¬ 
ficial furnaces made by us. Sir William Hamilton informs 
us, that the lava of Vefuvius, at the place whence it if- 
fued (in the year 1767), “ had the appearance of a river 
of red-hot and liquid metal, fuch as we fee in the glafs- 
houfes, on which were large floating cinders half lighted, 
and rolling over one another with great precipitation 
down the tide of the mountain, forming on the whole a 
mod beautiful and uncommon cafcade.” Now, if we con- 
fider the materials of which the lava confifts, which un¬ 
doubtedly are the common matters to be foupd every¬ 
where in the earth, namely, (tones, metallic ores, clay, fand. 
See. we (hall find that our hotteft furnaces would by no 
means be able to bring them into any degree of fufion ; 
fince the materials for glafs cannot be melted without a 
great quantity of very fufibie lalts, fuch as alkalies, nitre. 
See. mixed along with them. The heat of a volcano mud 
therefore be immenfe ; and, befides its heat, it is fome¬ 
times attended with a very uncommon circumftance ; for 
fir William Hamilton informs us, that “the red-hot (tones 
thrown up by Vefuvius on the 31ft of March, 1766, were 
perfectly tranfparent ;” and the like remark lie makes on the 
vaft fitream of lava which iflued from the (ame volcano in 
1779. This we cannot look upon to be the mere effe<ft 
of heat; for mere heat with us will not make a folid body 
tranfparent ; and thefe ftones, we are fine, were not in a 
ftate of fufion, or the reliftance of the air would have 
broke them ail to pieces, even fuppoling them, which is 
very 
