106 
The Queensland Naturalist April, 1936. 
volcano that of Mont Pelee in the West Indies. Here 
the lava, as a result of its chemical composition, was so 
viscous that instead of flowing over the surrounding 
land it was forced up and up, higher and higher into 
the air, until Anally it formed an almost needle-like pro- 
jection over seven hundred feet above the crater. It is 
probable that our Glasshouses in Southern Queensland 
represent the relics of volcanic mountains similar to 
Mont Pelee, as do the bell-shaped domes of Auvergne in 
France. 
Of course, not all volcanoes are simply ash cones or 
Java cones. Many, including some of the largest, are 
made up partly of fragmental material and partly of lava 
flows. Such composite volcanoes also give rise to 
conical mountains. Some of these are, naturally enough, 
somewhat irregular, but others are among the most 
graceful and beautiful mountains of the world. The 
lavas from these volcanoes are sufficiently viscous to 
prevent their spreading very far, while the larger of the 
ejected blocks also tend to accumulate around the 
crater. But the relatively finer ash falls progressively 
farther from the centre of eruption. Since each of these 
grades of material has its own angle of rest, there is 
thus built up a mountain with a very characteristic pro- 
file. From the lip of the crater the slope is at first steep, 
at say 30 degrees, but as the distance from the crater is 
increased and finer material is encountered, the angle 
of the slope gradually diminishes until towards the base 
it is almost horizontal. The graceful curve thus 
developed is well illustrated by the world-famous Fuji 
Yama — the sacred mountain of Japan — but it is almost 
equally well developed in many other large volcanoes. 
But in spite of their many and obvious differences, 
all volcanoes have this much in common, they transfer 
heated material from the interior of the earth to the 
surface . To understand how this is done we must in- 
vestigate two main features, namely, the nature of the 
reservoir from which the volcanic products are obtained 
and the processes by which this material is propelled 
to the surface. Let us first inquire into the nature of 
the reservoir. 
One early idea based on the Nebular Hypothesis was 
that the earth, beneath a thin solid shell, was entirely 
molten, thus providing one enormous source of supply 
for volcanic eruptions. The evidence against this simple 
concept is so strong that it has been almost universally 
abandoned. 
The supporters of the Planetismal Hypothesis argue 
that the earth is solid throughout with the exception of 
