108 
The Queensland Naturalist April, 1936. 
entertaining) except to mention the common belief that 
volcanic eruptions were due to the action of violently 
raging winds imprisoned in the bowels of the earth. 
Coming to more modern times we see first the ten- 
dency to regard volcanoes as “burning mountains” in 
a literal sense and as due to the combustion of such in- 
flammable materials as coal and petroleum. A later and 
more plausible explanation was based on the spontaneous 
decomposition of sulphur-bearing minerals and one in- 
vestigator in the year 1700 produced what he thought 
was a model volcano by making a paste of water, sul- 
phur, and iron filings and burying the mixture in the 
ground. The material soon began to swell and forced 
the ground above it into a dome, through cracks in 
which sulphurous gases were given off and other vol- 
canic effects simulated. 
Another early writer, convinced that ordinary com- 
bustion was out of the question, appealed to electricity 
as the source of heat. 
Sir Humphrey Davy, Professor Daubeny and other 
chemists held that volcanic activity was due to violent 
chemical reactions such as the oxidation of the alkalies 
and alkaline earths. 
Still another school among whose members were 
Humboldt, Lyell and Dana saw in eruptions the result of 
great quantities of "water contained in the molten lavas 
suddenly becoming converted into steam. Some thought 
that the contained water was part of the original con- 
tent of the lava, others suggested that it was rain water 
which had percolated through the ground just as it does 
to feed hot springs, while still others pointed to the fre- 
quent occurrence of volcanoes in or near the oceans and 
insisted that the water which caused volcanic eruptions 
originated in the sea. 
The last of these suggestions was widely accepted, 
although in its original crude form it was far from con- 
vincing. It was the physicist Arrhenius who in the 
beginning of the present century clothed this old idea 
in modern dress. Shortly stated, his hypothesis is as 
follows: — The sea floor acts as a semi-permeable mem- 
brane which allows the water to percolate downward 
but will not allow the molten rock to penetrate upward. 
Hence more and more water accumulates in the lava 
which is forced upwards in the pipe of a volcano until it 
reaches a position where the pressure is sufficiently low 
for the imprisoned water suddenly to flash into steam, 
thus producing a violent explosion. 
Whether the water originally came from the ocean 
in some manner such as this, whether it came from rain- 
