THE ERUPTION OF ETNA. 
451 
of sodium and potassium by mere contact witb water^ or 
a moist substance_, is too common an experiment with popular 
lecturers to dwell upon. Just let us set side by side the usual 
compositions of the chief volcanic mineral products : — 
Augite. 
Horn- 
blende. 
Felspar 
(Potash) 
Albite 
(Soda 
Felspar). 
Pumice. 
Obsidian. 
Silica (SiO'i 
54-15 
59-5 
65-69 
67-99 
62-04 
74-80 
Lime (CaO) 
24-74 
12-3 
1-34 
• • • 
1-31 
1-96 
Magnesia (MgO) 
18-22 
26-8 
« • • 
• • • 
-72 
•90 
Alumina 
• • ■ 
• • • 
17-97 
19-61 
16-55 
12-40 
Potash 
• • • 
13-99 
* • « 
3-66 
6-40 
Soda 
1-01 
11-12 
6-39 
(some- 
&c. 
&c. 
&c. 
&c. 
&c. 
times.) 
&C. 
In every case the original or combustible base is combined 
with oxygen. 
So far as I know_, this branch of inorganic chemistry is not 
in that state of advance that would permit of any definite 
scientific deductions being at present obtained from the 
combinations of the metal bases with the oxygen. Organic 
chemistry has taught us that organic products are in definite 
combinations in regular series^ and when one link is missing 
to knowledge_, it can be formulated and artificially produced. 
It seems to me that some such exact knowledge in inorganic 
chemistry ought to do much in unravelling the mysteries of 
volcanic formations. 
The condition necessary for Sir Humphry Davyds hypothesis 
is that the pure metallic bases should be situated at a sufficient 
depth to preclude the access of air^ for if air had had access^ 
it would long ago have imparted that oxidation to which vol- 
' canic action^ if due to them^ would be attributable. The great 
difficulty has been how to account at all for their elimination 
in a metallic form. I think^ however, that the effects of 
crystallization might be profitably considered in respect to the 
possibility of metals and other extraneous substances being 
extruded from crystallized rock-masses, such as quartz and 
granite ; for we know that salt is extruded from sea- water in 
the process of freezing, and that the great masses of arctic 
ice, frozen from the ocean, are composed of water perfectly fresh. 
Sodium, silicon, potassium, calcium, magnesium, may have 
been extruded in the crystallization of hypogene rocks, and 
have formed large and dense beds where the crystallizing 
operation has been carried on during vast ages, over enor- 
mously thick and vast geographical areas. Does not the 
VOL. IV. — NO. XVI. 2 H 
