338. 
San Lorenzo, derive their origin from the 
fame vapours, which at this time fupply 
thefe baths; and that their fubterraneous 
arches will be found in procefs of time 
laden with fimilar depofitions. This, as 
has been already noticed, has happened 
in the Zolfatara of Pozzuoli (f. 7.). 
(18.) The filiceous fiala€tites above re- 
terred to of San Lorenzo, imbibed them- 
felves (i. 5.) in pumice, and thofe only 
of Monticeto (f. 9.) are adherent to a 
decompofed pumice rock; it may be 
‘added, that thofe greater ones of Monta- 
miata are found alfo ina friable granite 
vich in {mall pumice-ftones ; or cryftals 
of Feldfpar fwelled and cracked by fire, 
and hencesbecome fluid, as far as the en- 
tité mafs of granite is capable of becom- 
ing; as has been already obferved before 
mé by Count Dolomieu, and has been il- 
lufirated by him in his Voyage to the Ifles 
of Ponza. 
Indeed, when IT faw by means of the 
lens that this granite inclofes often in its 
fAbrous vein, produced as already fated, 
the minuteft filhceous and tran/parent 
ftala€tites, at fir I hefitated to believe 
that they were owing ftrictly to the dry 
fufion of feldfpar; but -fince that I am 
bécome acquainted with vapours, humid 
and faline, already formed or growing 
from thin elements reciprocally in ac- 
tivity, intimately diffufed through the 
mafs of ignited and running lava, and re- 
fleting how much fo {pungy a granite 
is penetrable by fuch vapours, I quit my 
firft idea as fuperfluous, if not erroneous ; 
expofing my own difficulty as a greater 
c2ution to him who wifhes to follow with 
the neceffary accuracy this argument. It 
does not appear to me, that the faid fta- 
latites have actually their erigin from 
pumice in preference to the other filiceous 
faubftances compefing fuch rock, but be- 
caufe the pumice may have prefented to 
the folvent vapours a fuperficies the moft 
multiplied, and, on that account, the melt 
capable of being generally attacked. 
(19.) Befides this, it may be noted 
fo tar as regards fulphur, that 
t..Some warm fprings in the vicinity 
of Geyfer give us filiceous depofitions 
mixed with fulphur. 
2. The little lakes of Saffe in Tuf- 
cany produce fulphur. 
3. Wefuvius in activity ‘gives ful- 
phur. 
4a. The filiceous ‘ftalaétites of the 
Meontamiata, thofe found by Abbate 
Breiflak in Tichia, and, finally, thofe of 
the Zolfatara di Pozzuoli, are all mixed 
with fulphur, 
Dr. Thompfon, Pr.....Utility of Prebendaries, 8 ts 
5. Although the orifices of Monti-- 
ceto, and of Ii{chia, have not as yet afforded 
aétual fulphur, there are, neverthelefs, 
fufficiently plain indications of it, in the 
prefence of vitriolic acid. exifting as well 
inthe alum as in the chalk found there 
(f, 10.); and alfo im bitter falt, both that - 
with a magnefian bafe, Epfom falt; or 
with a bale of mineral alkali, glauber 
falt, or finally of vegetable alkali, which. 
lat falt, vitriolated tartar, fo frequent 
upon the lavas which have dettroyed the 
plain, is not unknown in the higheft parts 
of Vefuvius, fince I have found it three 
years ago diftilling from the cone itfelf, 
half way from its bafe, from fome mouths 
whence a fmall ftream of lava has pro- 
ceeded, at no remote period. ‘This falt 
afterwards became fo hard, forming 
opaque mafies, fimilar to marble, that it at 
firft gave little fufpicion of its true na- 
ture; and, infact, I have feen it-defcribed 
in colle€tions, as ftones of Vefuvius. 
With regard to the bitter falt of 
Monticeto ({. 10.), its {carcity has not 
permitted us as -yet to afcertain its pre- 
cife nature. 
The preceding obfervations, there- 
fore, {fo nearly correfpond, as in effect to 
teach us, that wherever thefe filiceous 
ftalagtites have hitherto been found, we 
likewife meet with humid and warm 
vapours, with mineral alkali, often de- 
monftrated ({. 11.14. 15.), and whofe pre- 
fence is always to be fufpe&ted, as the 
generative caufe of thefe ftalaétites, with 
the intervention alfo of fulphur, either in 
fubftance, or manifefted in its .produét, 
which “is vitriolic acid, as foon. as ful- 
phur, in an aériform ftate, comes in con- 
taét with the atmofphere, whence it at- 
tracts that dofe of pure air which it re- 
quires to enable it to affume its new pro- 
perties. 
tenet 
Parthenope ftudiis forentem ignobilis ott. 




me a , ‘ 
To ihe Editor of the Monthly Magazine. 
SIR, 
OUBTS have been fometimes enter- 
tained by men who ate in the habit 
of thinking for themfelves, concerning 
the utility of fome clafles of dignitaries 
in our church, particularly..deans and 
prebendaries. The opinion of .an arch- 
bifhop, therefore, upon this fubject, muft 
have contiderable weight: and the follow- 
ing curious obfervations, on the advan- 
tages refulting from prebendaries to reli- 
gion and learning, are contained in a let- 
ter 
