April, 1936. The Queensland Naturalist 
109 
water soaking through the ground or whether it was 
always present in the lava geologists are generally agreed 
that the more explosive manifestations of* volcanic activ- 
ity are due to the sudden liberation of enormous quan- 
tities of steam. 
But what of those very different eruptions where 
great quantities of very fluid lava quietly well out of 
Assures and flow like water over the land? By their 
very nature these appear as if they were squeezed out 
rather than blown out and it seems almost certain that 
they are due simply to displacement. Indeed, many 
geologists think that the major control behind all vol- 
canic phenomena is pressure of this type due to the rela- 
tive movements of great blocks of the earth’s crust. In 
support of* this contention they pont out that volcanoes 
commonly occur along the margins of the continents, 
each continent probably representing one great block and 
its coastline representing the hinge line between it and 
the. neighbouring oceanic block. Thus J. W. Gregory is 
of the opinion that “The distribution of volcanoes shows 
that they are formed where sinking blocks of the crust 
exert such heavy pressure on the plastic material below 
that it is forced to the surface up the fractures around 
the sinking areas.” 
But while the general upward movement of lava 
may be brought about in this way, the immediate cause 
of eruption, especially of the more violent volcanoe 
seems to be due to the explosive action of high-pressure 
steam. 
This combination of earth movement and steam 
pressure is the most satisfactory attempt yet put for- 
ward to explain this complex problem, nevertheless some 
modern workers are far from satisfied with it and at the 
present time two much more complicated hypotheses 
are in process of elaboration. 
One attempts to explain volcanoes in terms of radio- 
activity, the other in terms of a supposed convectional 
circulation of the molten matter of the interior of the 
earth. It is too early yet to say ivhether either of these 
is capable of solving all the manifold problems presented 
by the mechanism of volcanoes. 
CENTRAL QUEENSLAND, EASTER, 1935. 
A SHELL COLLECTING TRIP IN KEPPEL BAY, 
(By H. Bernhard.) 
North Keppel Island lies 12 to 15 miles east of the 
mainland coast and possesses a fauna that is distinct 
from that of the mainland on the one hand and the Great 
