April, 1936. The Queensland Naturalist 
107 
a number of tongues of molten material which are 
arranged radially, like the spokes of a wheel and that it 
is these liquid tongues which act as feeders to the vol- 
canoes. There are many theoretical objections to this 
hypothesis, so that it is rapidly declining in favour even 
in the United States, the land of its birth. 
A less objectionable theory, from the physical point 
of view than either of the preceding, and one that has a 
considerable number of adherents at the present day, 
holds that there is a continuous zone of molten material 
sandwiched between the solid outer crust and an equally 
solid centre. To many authorities, however, the way in 
which earthquake waves are transmitted appears to pre- 
clude any completely liquid zone. 
This difficulty was overcome, but fresh ones were 
created by the suggestion that each volcano was sup- 
plied independently from its own particular reservoir 
set in an otherwise solid zone. But such a view of com- 
plete independence of neighbouring volcanoes is hardly 
in keeping with the history of many volcanic regions. 
A more modern picture of the zone immediately 
beneath the solid crust shows us a sort of honeycomb or 
sponge-like structure made up of an irregular solid 
framework tilled with a more or less continuous mass of 
liquid lava. 
One general scheme which has found wide support 
is based on the supposition that, below the solid crust, 
there is a zone of material almost at the melting point 
so that a slight change in conditions may bring about 
local liquif action and thus provide a reservoir for an 
overlying volcano. Such a change from solid to liquid 
might be brought about either by relief of pressure or 
by an increase of temperature. In the former case, the 
relief of pressure might result from the arching upwards 
of a portion of the solid crust or by some other earth 
movement on a large scale. In the latter case liquefac- 
tion might be brought about, as suggested by Professor 
Joly, by the slow self-heating of the mass due to the 
radioactive transformations continually taking plac^ 
within it. 
Since it seems impossible at present to decide on 
the precise nature of the volcanic reservoirs, we must be 
content with the knowledge that there are below the 
active volcanoes sources of supply. 
Our next inquiry concerns the manner in which the 
various volcanic substances are carried to the surface 
and there ejected. 
Space does not permit us to examine the views of 
the ancients on this subject (although they are vastly 
