330 NOTICES OF THE MEETINGS [June 3, 
substances preclude them from being regarded as real volcanic 
products. 
The springs of Iceland permit of being divided into two great 
classes; one class turns litmus paper red, the other restores the 
colour; one class is acid, the other alkaline. Periodical erup- 
tions are scarcely ever known to occur among the former, while 
to the latter belong the Geisers of the island. Here then we have 
two facts which form the termini of a certain chain of opera- 
tions — the water of the clouds and the water of the spring: in 
its passage from one terminus to the other is to be sought the 
cause of those changes which the water has undergone. 
In seeking insight here, experiment is our only safe guide. Let 
us endeavour to combine the agencies of nature, and see whether 
we cannot produce her results. Sulphurous acid is one of the most 
important gases which the water encounters in its passage. Now 
if a piece of palagonite, the rock through which the water filters, be 
heated with an excess of aqueous sulphurous acid, it dissolves in the 
cold to a fluid coloured yellow brown by the presence of peroxide 
of iron. On heating the fluid this peroxide is converted into 
protoxide; a portion of its oxygen goes to the sulphurous acid, 
forming sulphuric acid, which combines with the bases of the rock 
and holds them in solution. This is the first stage of the fumarole 
process. But if the process ended here, we might expect to find the 
dissolved constituents of the rock in the resultant spring, which i 
by no means the case, as a glance at the following table will shew. 
RELATION OF BAsEs. 
In Palagonite. In the Suffion water. 
Oxide of iron * : 36.75 : - 0.00 
Alumina . : i 25.50 BY Rte 12.27 
Lime r . , 20.25 j : 42.82 
Magnesia. 3 : 11.39 ; : 29.42 
Soda ; z 3 3.44 i lu 9.51 
Potash : B i 2.67 : 5.98 
100.00 100.00 
We see here that the rock contains a large quantity of the oxide 
of iron, while the spring does not contain a trace of it. It is, how- 
ever, an experimental fact that the oxide of iron has been dissolved 
with the rest. How is its disappearance to be accounted for? The 
very rock from which it was originally extracted possesses the 
power of re-precipitating it, when by further contact with the rock 
the solution which contains it has its excess of acid absorbed and has 
thus become neutral. In this way the aqueous sulphurous acid acts 
asa carrier to the iron, taking up its burden here and laying it 
down there ; and this process of transference can be clearly traced 
