90 
GEOLOGICAL QUERIES. 
selves to ideas generally interesting, and seek, in the study 
of nature, for answers to the following questions 
Is the conical mountain of a volcano entirely formed of 
liquified matter heaped together bv successive eruptions, 
or does it contain in its centre a nucleus of primitive rocks 
covered with lava, which are these same rocks altered by 
fire? What are the affinities which unite the productions 
of modem volcanoes with the basalts, the phonolites, and 
those porphyries with bases of feldspar, which are without 
quartz, and which cover the Cordilleras of Peru and Mexico, 
as well as the small groups of the Monts Dores, of Cantal, 
and of Mezen in France ? Has /he central nucleus of vol- 
canoes been heated in its primitive position, and raised up, 
in a sottened state, by the force of the elastic vapours, 
before these fluids communicated, by means of a crater, with 
the external air? What is the substance, which, for thou- 
sands of years, keeps up this combustion, sometimes so 
slow, and at other times so active P Does this unknown 
cause act at an immense depth ; or does this chemical action 
take place in secondary rocks lying on granite ? 
The farther we are from finding a solution of these prob- 
lems in the numerous works hitherto published on Etna and 
Vesuvius, the greater is the desire of the traveller to see 
with his own eyes, lie hopes to he more fortunate than 
those who have preceded lnm ; he wishes to form a precise 
■dea of the geological relations which the volcano and the 
neighbouring mountains hear to each other: but how often 
is he disappointed, when, on the limits of the primitive soil, 
enormous hanks of Infix and puzzolana render every observa- 
tion on the position and stratification impossible ! We reach 
(he inside of the crater with less difficulty than we at first 
expect ; we examine llie cone from its summit to its base ; 
x\e arc struck with the difference in tho produce of each 
eruption, and with tho analogy which still exists between 
the lavas of the same volcano; hut, notwithstanding tho 
care with which wo interrogate nature, and tho number of 
partial observations which present themselves at every step, 
we return from the summit of a burning volcano less satis- 
fied than when we were preparing to visit it. It is after we 
have studied them on the spot, that the volcanic phenomena 
